I used to run 2 Sapphire 5830s at 950/300 for stability under Windows. I found a tool called aoclbf and I used it for over/underclocking and it also has a way to configure miners. I had more luck with GUIMiner and phoenix and got around 310 mh/s from each card. Temps stayed in the 70s and each card needed around 140 W from the wall if I remember correctly.
Cool, that sounds great. I have clocked down the memory, saved a TON of heat, fans stay really low. However, my 5830s average around 280-290 mh/s in cgminer, I might try GUIMiner with phoenix and different mining programs to see if I can get any higher. Thanks for the info!