Best way to overclock/underclock/over volt my Sapphire 6870, What tags?

[celcoid]

Hello I would like to find out how to get max Mhash on my 6870 should I underclock the memory? How High is it save to overclock at what voltages? What tags should I use? Im using GUIminer.

[TeaL]

If you're using Windows, you should be able to modify core clocks, voltage, and fanspeed in the Catalyst Control Centre. As for underclocking memory, I don't use Windows so I can only recommend you search for a tool, perhaps someone else here knows of one. 

[RyNinDaCleM]

Use this guide
Or Sapphire trixx

For flags; I use -v -w128 for all 5xxx/6xxx GPUs except 5830s!

[iopq]

Use this guide
Or Sapphire trixx

For flags; I use -v -w128 for all 5xxx/6xxx GPUs except 5830s!

you should use -w256 and underclock ram, there's a sweet spot that's faster than 128 and stock

[vapourminer]

not exactly the same card, mine is an asus directCU 6870. stock volts, cant help there.

sdk 2.4, 11.6 drivers, guiminer with "-v - w 128 -f 20"

@ 1010 core it pulls 300 MHs, temps are 70s with fan @ 75%, closed case. but I had to replace the stock thermal junk with artic cooling TX2. memory is about stock as this is the main "goto" computer in the house.

[RyNinDaCleM]

Use this guide
Or Sapphire trixx

For flags; I use -v -w128 for all 5xxx/6xxx GPUs except 5830s!

you should use -w256 and underclock ram, there's a sweet spot that's faster than 128 and stock

-w128 works the best for mine!
My 6950UL'd is at 935/1000 -w128 417Mh
2x 5830 990/450 -w256 315Mh each
3x 5770 1000/350 -w128 225Mh each
1x 5850 1000/400 -w128 400Mh
I think these are pretty good results!

[johnj]

3x 5770 1000/350 -w128 225Mh each

I'm at 1000/300 -v -w256 @227Mh each.  And using Phoenix I'm at 231Mh each.

Not much different, just throwin that out there.

[n4l3hp]

Running 2 Sapphire 6870 at 310Mh/s (970/300). Was able to get 323MH/s at 1020/300 (1.25v) but consumed about 20w more per card.

-v -f 10 (got same performance with or without -w 256)

I'm using the 890 IGP as primary video. Tried -f 0 but browsing with google chrome is a pain. The mouse cursor movement was a bit jumpy.

Edit: There is also a 5670 at 112MH/s (1000/150) running with the 6870s using the same flags.

[Roddy5690]

I'm getting 25 M/hashes more thanks to this thread , my settings are 995 GPU clock, 1050 memory clock.