One 6850 isn't going to cut it. Go ahead and Crossfire the 6850s. Are they the 1gb or 2gb versions? The 1gb versions will be bottlenecked by vram so you'd want to keep your texture res and AA down low (AA off probably). They'd do ok but settings would have to be pretty low. The 2gb cards would be a lot better, but still just ok. The bottom line - Crossfire them and enjoy eyefinity - when you want higher settings and/or more frames then save up and buy more powerful cards with more vram.