Sorry ordcestus, but that calculator on newegg is WACK! In no way shape or form do you need 800w for an SLI 8800GTX setup. When the 8800GTX SLIs hit the market, there weren't 800w PSUs.
A pair of 8800GTXs will eat 231w measured from the card.http://mark.zoomcities.com/images/gfx/GFXpowerchartby3d.png
The CPU if OC'd will eat 150ish, 75w for the rest. Confirmed by this PSU calculator:http://www.antec.outervision.com/PSUEngine
That's 375w load, and rarely will all your components be loaded at the same time. The Corsair 650w is more than enough for that SLI setup. Corsairs are top notch and will actually provide more than 650w, so yours will still stay in a decent efficiency envelope even if you're pulling 60% of capacity.
I'm part of Proximon's team developing a PSU ranking list in the 1000w+ section. See the link in my sig. If you need more EVIDENCE besides an etailer that's trying to sell you more than you need, I will be happy to provide even more links.