Minimum PSU for 6800 cards is 350W, but with that amount of devices, get 400W or better. Antecs are probaply best choice since they are stable AND very silent, since they have big fan on bottom sucking air from case instead small screaming fanny running 100000rpm on back. They are again quite costlier. It seems that my cheapy COLORS-IT 400W is source of instability for me... I dunno, i have to test it...