I have 3x 6950's currently running on a single Corsair TX850... no idea what the power draw is on them though. It's also powering the rest of my LGA2011 box too, so I'd venture a guess it's pretty high. The only saving grace is that all three of those cards are undervolted to 1.025v.
I have 4 on an EVGA 750w gold just fine. I can check power draw at the wall later