Thanks Jemm, I was also thinking that a 600W PSU should be enough, but not all power sources are created equally. The Antec High Current Gamer Series 620W can carry 576W on its single 48A 12V rail. The problem is that a single HD 4890 can use up to 190W @ 16A when overclocked. I am just as concerned with amperage as wattage and knowing that the crossfire setup could use 32A causes me to worry because I don't know how many amps my system needs. In general I am not very tech savvy when it comes to in's and out's of electric current.