~320mhash here with a sapphire 6950 2gb, with unlocked shaders (NOT 6970 bios, just unlocked shaders), @840mhz. Catalyst 11.3. Anything faster was unstable and I dislike experimenting.
poclbm_py2exe_20110325\poclbm.exe --device=0 -v -f 2 -w 64
I say ~320mhash because it really depends on the -f switch. If I use -f 2, I get up to 328 mhash, but everything else lags this way, it's only really possible to use it during sleep. With -f 120 I get absolutely no lag ever, but the speed varies from ~290 to ~310, depending on how much "activity" is on the screen. If I'm running apps that update the screen often, even something like a visualizer in an audio player, the hashrate may fall more. Increasing the -f switch will keep the hashrate up, but then the screen will lags cause poclbm will hog all the videocard horsepower.