Come over here to my place in Farmington, Michigan and I'll provide the beer while you tweak my 5870 OC to the max!
No more of this "1 BTC reward" business, beer! Actually, I've seen the 5870 thread, I'm running up on the stability limit at stock voltage, is +10% on voltage still a safe rule of thumb?
I use stock voltages with all of my 58xx cards (indeed I use 58xx cards exclusively), downclock memory to 300MHZ, and push the cores as high as the temps will allow. Pity I had to shut most of my rigs down due to the heat here. My desktop with duo 5850's still runs like a champ pushing 380 MH/s each though.