BFG Tech GTX275 OCX SLI Power Requirements?

Hey guys, first time poster here. I'm alright with tech stuff, but definetely still learning. I built a system 4 years ago for college, and now that I'm about to graduate I'm treating myself to a new system. I am planning on the i7 920, and have ordered one of these 275 cards already (BFG Tech GTX 275 OCX), but I plan to get another one in SLI in a few months. I'm looking at a SeaSonic 850W power supply. I like this power supply because in reviews it's one of the most efficient supplies tested (over 90%), and it still has pretty good wattage. I just want to be sure that this supply will power an i7 with two OCX GTX275's in SLI.

Thanks for your responses in advance. I'm sure I'll be asking many more questions for this build.