he right i was doing about the same with a 850 watt gold PSU i was hitting 562 watts at the wall with three 470 and one 480 but mine are modded to use less power and hash more i can probable get more out of them at a cost by max over clocking and hope i don't make them to unstable , il play it safe i found my sweet spot.


or
 689 sol using 562 watts at the wall with only one 480 so if i had two ID be close mine are all 4gb cards so it would be close.