A Silverstone 850 is a pretty nice PSU, though. Nothing wrong with it.
580 SLI under Furmark load uses 777W! Yeah, I'd say an 850 might be OK, but 1000W would be safer.
The 480 is even worse. I can't wait to ditch this card, but I don't want to ditch it for a 580 just for a marginal update in speed. Even the 580 uses a lot of power.