since there performace is pretty much the same there price should be the deciding factor.dont pay 100$ extra for just a nominal increase in performace.personally i would tend to lean toward the geforce 6800 ultra because of its shader model 3.0 and nvidia brand.but i should also mention 2 things about this card,one it requires a beefy psu (480 w or higher)through one or two molex connector on the card itself for power.also it is a little big on the size so it can easily take up/cover up the space for the pci slot.x850 however i havent seen or checked so i am unsure there,so checkthese two things too.