It is possible for a 6950 to beat a Stock GTX 580 & tie/beat GTX 580 SC.
I have my MSI R6950 Twin Frozor unlocked to 1536 shaders (same as the 6970),
and overclocked well over 880/1375 default 6970 clocks.
to beat a GTX 580 in terms of 3DMARK 11 Score, you must have your 6950 unlocked or 6970 clocked at about 940/1450, to beat/tie a GTX 580 SC, about 1000|1500.
You would need MSI Afterburner to bump up the voltage, also watch your temperature, i don't recommend going over 80C on the GPU.
Mine hovers 76-79C on 1hr of furmark. Graphic card is rock solid. I'm probably lucky. Air cooled
set the power control on CCC to +20% so that your graphic card's memory and core won't dip down in frequency when it is under load.
If you googled "GTX 580 3DMark 11 Scores" mine would be with the 580's.
Message edited by trihedral on 09-01-2011 at 08:13:43 AM