Tread carefully here... you're traveling amongst the world of specsmanship... I suggested the Corsair 750 due to real world experience, not as a result of examining the "specs"... my systems has had as many as 14 drives, not earth shaking, but substantial... I've had two other power supplies in it, an OCZ 600 watt and a Seasonic 650 watt... with both supplies (mostly with the OCZ) the machine would re-boot when I hit the button to spin up all drives. Power calculations aside, as they predicted "no problem ", I think actual results count for a lot more credibility.... I can only say that the Corsair 750 runs cool (speaks to efficiency) and doesn't sag under load... YMMV