I was using the single slot powercolor one until i got a different mobo. got about 280 out of it stocvk voltage... memory was at 445 (anything lower caused issues) probably can get more with latest kernels though...
I stopped using it, need to sell it now...
Are you talking about a single slot 6850 getting 280mh/s? I don't see it feasible. I have 3 and I'm lucky to get 240 out them. Even at that they crash the system once every 4-5 hours.