Hmm, if you are using Stilts' BIOS u can also try 1375MHz Mem and adjust core clocks accordingly.

If your card is throttling even at 73C check your VRM temperatures in GPU-Z, if that is hitting 90C+ that might be the problem. Try turn the Power Limit to -20% might help.

Keep in mind sometimes higher clock doesnt result the highest hashrate. go from 900 Core clock and add 10Mhz each time if hashrate goes up try bump 10 more until you hit the point where it start dropping or your card is running too hot. try to keep it under 80C

Adding a strong fan blowing directly at top of the card or the back of the card will reduce VRM temptures try that.

my 7970s run @ 1050/1500/1.087V

Use GPU-Z to check your VRM temperature, for mining you want to use as low voltage as possible that will greatly reduce VRM stress and power consumption.
When you are mining the first to overheat is your VRM if there is no steps taken to lower your voltage and additional cooling fans at the back of videocard.
most likely the reduced hashrate is because VRM overheat and throttling down the core speed.

Worst case scenario it will heat up to much your video card caches on fire. according to the stilt some XFX cards have really cheap VRM controller (analog instead of digital) to save cost.

You can use VBE7 to modify BIOS voltage or use software like MSI Afterburner to lower voltage. You can start by lower the powertune to -20%

Try this BIOS out:
http://www.mediafire.com/download/8dldldm58wxqrs2/MBA_C3860100-100_AGR_K2.rar
it should work well with any reference design card!
Same stuff as always 1500MEMCLK only and adjust core&voltage to your liking.

good to hear, how much are you getting now with what clocks? I'm currently running 1050/1500 @ 730KHs. 1070/1500 can get me 750KHs for about 15 min and it lowers to 730 for some reason, so I just lowered clock to 1050 and it hashes 730KHs happily.
anything is appreciated

tip received thanks ! that was my first income since I started mining LOL.


EDIT: I found another Modded BIOS for the card going to try it out later when I get home today, will keep you updated! Happy mining
EDIT2: Well the BIOS I found pretty much perform on-par with the last BIOS i posted. I'm gonna try out 13.12 driver see if any difference with that.
EDIT3: 13.12 and 13.1 perform same. So I pretty much hit the ceiling for now at 730KHs/s on this powercolor reference.

The one I posted above is my BIOS, Keep your mem clock at 1500
and adjust core from 1000 and higher I'd say for my card 1020/1500 - 1070/1500 is the best performing clocks.
Use AMD uninstaller to uninstall all drivers and download 13.1

you have the AFR vram which according to The Stilt has the correct timing built in. I got the MFR which is the rubbish timing. But I already got a modded bios which can get me 750KHs so I'm good! But thanks.

lol really only 4? what settings have u tried and what drivers are you running?
also give me a screenshot of the flashed card with gpu-z

Update for ya, I found a ASUS 7970 bios modded by The Stilt that can boost my card up to around 711KHs. I'm still testing the stability will keep u informed very soon, still finding the highest hash rate so far.
Also I changed my minier to sgminer 4.1.0 as that's the newest miner available, Driver still 13.1. script:

EDIT: also when your increasing your core clock and hash rate goes up that's a good sign, keep going up til u hit the point where it DROPS. and that last clock where it didn't drop is the sweet spot.

EDIT2: After a few hours of tuning I have gotten my card to run at 750KHs @ 1070/1500/-20% Power tune/80% Fan @ 73C. Gotta say I'm pretty satisfied. The card seems to be able to handle even higher speed but I'm playing it safe as 1070 is already fairly high clock.

For this BIOS MEM CLK stays @ 1500 as specified by The Stilt due to the BIOS contains modified CL timing. Just raise your clock from 1000 with 10 increment til it either drops or if temp is reaching GPU ~80C /VRM ~90C. My still goes up even after 1070 But like I said, I want choose this place to stop at around 750KHs for safety.

BIOS:
https://www.dropbox.com/s/cgaaubvsnw9uh0w/7970MOD.bin

HP USB Disk Storage Format Tool:
http://download.cnet.com/HP-USB-Disk-Storage-Format-Tool/3000-2094_4-10974082.html
WIN98 Boot:
http://www.bay-wolf.com/utility/usbkey/win98boot.zip
ATIFLASH 4.17:
http://www.techpowerup.com/downloads/2306/atiflash-4-17/

If you don't know how to flash heres the post where I learned it:
http://forums.guru3d.com/showthread.php?p=4503953

PS: My card is Powercolor AX7970 3GBD5-M2DHV2, with SK Hynix H5GQ2H24MFR VRAM Chips. Have the reference AMD red/black Turbine cooler.
PSS: when you are putting the atiflash.exe in the usb its easier to name it shorter as DOS tend to shorten it as ATIFLA~1.exe which is a PITA to type.
PSSS: back up your current BIOS from GPU-Z and name it 7970Ori.rom so you can flash back in case of failure. Flash the BIOS 1 on the card. the switch is near the CF bridge.

Hope this helped you! I'm still waiting to sell my gaming machine for money so I can get a mobo that can run all 3 of my cards together haha. Right now only one card its sitting in this old HP machine with AMD 4600+, 4GB DDR2 533 RAM and an Antec 450W PSU and it still hashes 750KHs without a sweat xD

I have 3 of the exact same cards. Just got them yesterday to begin my mining rig. So far I have only 1 card running as my motherboard is yet to arrive. as for the settings I'm running :

Catalyst 13.1 clean install. with included APP APK.
Win 7 Ultimate 64Bit
CGminer 3.1.0


Now this will get me anywhere from 520-560kh/s speed on the card if I leave the card at default clocks. BUT after hours of tuning with just AMD Overdrive, I gotten my hasrate up to 660Kh/s

945-949/1575 = 650KHs
895-899/1500 = 625KHs

mem clock is set to max for the best efficiency mining and the core clock has a very sensitive line.
For example my card will get around 550KHs with 950/1575 and 650KHs with 945/1575
Because AMD Overdrive only does 5Mhz increment I cannot pin point the exact line to the 1Mhz yet.
You can play around with ur Core clock a bit with one card and try to find the line that gets u that extra 100 Khs

Since 650KHs is still probably a bit off from the optimal speed for a 7970
My next step would be trying to find more BIOS for the card but I havent started on that yet!