Hi, received the app and it works great.  
EDIT: Summary of tests, all were able to underclock memory to 300mhz.
XFX HD5850 Win7 64bit,  -v range is 951 to 1100 in steps of 1
HIS HD5770 WinXP 32bit,  no voltage control, fan speed reports unknown
Sapphire HD5750 Win7 64bit, -v appears in to be steps of 1, did not test full range.
Would like two feature requests:
1) ability to control fan speed from command line.  This way I can script idle/mining/gaming and control temps a little better.
2) bare format (suppress program name and version) that shows date/time and all adapter details in one line, would like to be able to run this every 5 mins and dump to a text file for logging/monitoring
XFX HD5850, 2 monitors attached, Win7 64bit
C:\Program Files (x86)\clocktweak>clocktweak -x
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Exploring up to 20 adapters:
A.#:0  r:0 ID:50299136  Name:"ATI Radeon HD 5800 Series"  Active:1  GPU:0
A.#:1  r:0 ID:50299136  Name:"ATI Radeon HD 5800 Series"  Active:1  GPU:0
A.#:2  r:0 ID:50299136  Name:"ATI Radeon HD 5800 Series"  Active:0  GPU:0
A.#:3  r:-1 ERROR: explore_adapters: adapter  3 could not be initialized (-1)
A.#:4  r:-1 ERROR: explore_adapters: adapter  4 could not be initialized (-1)
A.#:5  r:-1 ERROR: explore_adapters: adapter  5 could not be initialized (-1)
A.#:6  r:-1 ERROR: explore_adapters: adapter  6 could not be initialized (-1)
A.#:7  r:-1 ERROR: explore_adapters: adapter  7 could not be initialized (-1)
A.#:8  r:-1 ERROR: explore_adapters: adapter  8 could not be initialized (-1)
A.#:9  r:-1 ERROR: explore_adapters: adapter  9 could not be initialized (-1)
A.#:10  r:-1 ERROR: explore_adapters: adapter  10 could not be initialized (-1)
A.#:11  r:-1 ERROR: explore_adapters: adapter  11 could not be initialized (-1)
A.#:12  r:-1 ERROR: explore_adapters: adapter  12 could not be initialized (-1)
A.#:13  r:-1 ERROR: explore_adapters: adapter  13 could not be initialized (-1)
A.#:14  r:-1 ERROR: explore_adapters: adapter  14 could not be initialized (-1)
A.#:15  r:-1 ERROR: explore_adapters: adapter  15 could not be initialized (-1)
A.#:16  r:-1 ERROR: explore_adapters: adapter  16 could not be initialized (-1)
A.#:17  r:-1 ERROR: explore_adapters: adapter  17 could not be initialized (-1)
A.#:18  r:-1 ERROR: explore_adapters: adapter  18 could not be initialized (-1)
A.#:19  r:-1 ERROR: explore_adapters: adapter  19 could not be initialized (-1)
valid adapters: [0, 1, 2]
gpuAdapters: [0]
Compatible GPUs found on these adapters:
Adapter#:0  ID:50299136  Name:"ATI Radeon HD 5800 Series"  Active:1  GPU:0
Reading data:
Adapter#:0 Temp:60 Load:96 Fan:75 Level:2
CoreL0:157 CoreL2:775 MemL0:298 MemL2:1050 mVoltL0:950 mVoltL2:1088
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -m300 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting mem speed: 300 [MHz]
Set values - finished.
Reading:
#0: Temp:60 Load: 0 Fan:74 Level:2 CoreL2:775 MemL2:300 mVoltL2:1088
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -v1087 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1087 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1087
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -v1086 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1086 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1086
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -v1085 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1085 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1085
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -v1050 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1050 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1050
C:\Program Files (x86)\clocktweak>clocktweak.exe  -a 0 -v1000 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1000 [mV]
Set values - finished.
Reading:
#0: Temp:57 Load: 0 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1000
Just a note.. after undervolting to 1000 I stabilized at 52C.
#0: Temp:52 Load:98 Fan:75 Level:2 CoreL2:775 MemL2:300 mVoltL2:1000
HIS 5770, 1 monitor, WinXP 32bit
No luck at all on undervolting.  Also can't see fan speed.
C:\Program Files\clocktweak>clocktweak.exe -x
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Exploring up to 20 adapters:
A.#:0  r:4 ID:-512820704  Name:"ATI Radeon HD 5700 Series"  Active:1  GPU:0
A.#:1  r:4 ID:-512820704  Name:"ATI Radeon HD 5700 Series"  Active:0  GPU:0
A.#:2  r:-1 ERROR: explore_adapters: adapter  2 could not be initialized (-1)
A.#:3  r:-1 ERROR: explore_adapters: adapter  3 could not be initialized (-1)
A.#:4  r:-1 ERROR: explore_adapters: adapter  4 could not be initialized (-1)
A.#:5  r:-1 ERROR: explore_adapters: adapter  5 could not be initialized (-1)
A.#:6  r:-1 ERROR: explore_adapters: adapter  6 could not be initialized (-1)
A.#:7  r:-1 ERROR: explore_adapters: adapter  7 could not be initialized (-1)
A.#:8  r:-1 ERROR: explore_adapters: adapter  8 could not be initialized (-1)
A.#:9  r:-1 ERROR: explore_adapters: adapter  9 could not be initialized (-1)
A.#:10  r:-1 ERROR: explore_adapters: adapter  10 could not be initialized (-1)
A.#:11  r:-1 ERROR: explore_adapters: adapter  11 could not be initialized (-1)
A.#:12  r:-1 ERROR: explore_adapters: adapter  12 could not be initialized (-1)
A.#:13  r:-1 ERROR: explore_adapters: adapter  13 could not be initialized (-1)
A.#:14  r:-1 ERROR: explore_adapters: adapter  14 could not be initialized (-1)
A.#:15  r:-1 ERROR: explore_adapters: adapter  15 could not be initialized (-1)
A.#:16  r:-1 ERROR: explore_adapters: adapter  16 could not be initialized (-1)
A.#:17  r:-1 ERROR: explore_adapters: adapter  17 could not be initialized (-1)
A.#:18  r:-1 ERROR: explore_adapters: adapter  18 could not be initialized (-1)
A.#:19  r:-1 ERROR: explore_adapters: adapter  19 could not be initialized (-1)
valid adapters: [0, 1]
gpuAdapters: [0]
Compatible GPUs found on these adapters:
Adapter#:0  ID:-512820704  Name:"ATI Radeon HD 5700 Series"  Active:1  GPU:0
Reading data:
Adapter#:0 Temp:44 Load: 0 Fan:N.A
Level:2
CoreL0:157 CoreL2:960 MemL0:298 MemL2:1200 mVoltL0:1200 mVoltL2:1200
C:\Program Files\clocktweak>clocktweak.exe -a 0 -m300 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting mem speed: 300 [MHz]
Set values - finished.
Reading:
#0: Temp:43 Load: 0 Fan:N.A
Level:0 CoreL2:960 MemL2:300 mVoltL2:1200
Tried values 1000, 1050-1199, 1201:
C:\Program Files\clocktweak>clocktweak -a 0  -v1199 -y
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1199 [mV]
ERROR: write_values: voltage 1199 could not be set (1)
C:\Program Files\clocktweak>clocktweak -a 0  -y -v1201
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1201 [mV]
ERROR: write_values: voltage 1201 could not be set (2)
And finally Sapphire 5750, 2 monitors, Win7 64bit:
C:\utils\clocktweak>clocktweak.exe -x
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Exploring up to 20 adapters:
A.#:0  r:6 ID:57783680  Name:"ATI Radeon HD 5700 Series"  Active:1  GPU:0
A.#:1  r:6 ID:57783680  Name:"ATI Radeon HD 5700 Series"  Active:1  GPU:0
A.#:2  r:6 ID:57783680  Name:"ATI Radeon HD 5700 Series"  Active:0  GPU:0
A.#:3  r:-1 ERROR: explore_adapters: adapter  3 could not be initialized (-1)
A.#:4  r:-1 ERROR: explore_adapters: adapter  4 could not be initialized (-1)
A.#:5  r:-1 ERROR: explore_adapters: adapter  5 could not be initialized (-1)
A.#:6  r:-1 ERROR: explore_adapters: adapter  6 could not be initialized (-1)
A.#:7  r:-1 ERROR: explore_adapters: adapter  7 could not be initialized (-1)
A.#:8  r:-1 ERROR: explore_adapters: adapter  8 could not be initialized (-1)
A.#:9  r:-1 ERROR: explore_adapters: adapter  9 could not be initialized (-1)
A.#:10  r:-1 ERROR: explore_adapters: adapter  10 could not be initialized (-1)
A.#:11  r:-1 ERROR: explore_adapters: adapter  11 could not be initialized (-1)
A.#:12  r:-1 ERROR: explore_adapters: adapter  12 could not be initialized (-1)
A.#:13  r:-1 ERROR: explore_adapters: adapter  13 could not be initialized (-1)
A.#:14  r:-1 ERROR: explore_adapters: adapter  14 could not be initialized (-1)
A.#:15  r:-1 ERROR: explore_adapters: adapter  15 could not be initialized (-1)
A.#:16  r:-1 ERROR: explore_adapters: adapter  16 could not be initialized (-1)
A.#:17  r:-1 ERROR: explore_adapters: adapter  17 could not be initialized (-1)
A.#:18  r:-1 ERROR: explore_adapters: adapter  18 could not be initialized (-1)
A.#:19  r:-1 ERROR: explore_adapters: adapter  19 could not be initialized (-1)
valid adapters: [0, 1, 2]
gpuAdapters: [0]
Compatible GPUs found on these adapters:
Adapter#:0  ID:57783680  Name:"ATI Radeon HD 5700 Series"  Active:1  GPU:0
Reading data:
Adapter#:0 Temp:47 Load: 3 Fan:N.A
Level:0
CoreL0:157 CoreL2:860 MemL0:298 MemL2:1160 mVoltL0:1000 mVoltL2:1100
C:\utils\clocktweak>clocktweak -a 0 -y -m300
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting mem speed: 300 [MHz]
Set values - finished.
Reading:
#0: Temp:46 Load: 0 Fan:N.A
Level:0 CoreL2:860 MemL2:300 mVoltL2:1000
C:\utils\clocktweak>clocktweak -a 0 -y -v1100
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1100 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:N.A
Level:2 CoreL2:855 MemL2:300 mVoltL2:1100
C:\utils\clocktweak>clocktweak -a 0 -y -v1099
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1099 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:N.A
Level:2 CoreL2:855 MemL2:300 mVoltL2:1099
C:\utils\clocktweak>clocktweak -a 0 -y -v1098
===============================================================================
                ClockTweak v0.7.4b - bitcoinX.com/clocktweak/
===============================================================================
Set values - starting.
 Adapter #0:
  setting voltage 1098 [mV]
Set values - finished.
Reading:
#0: Temp:58 Load: 0 Fan:N.A
Level:2 CoreL2:855 MemL2:300 mVoltL2:1098