Thanks so much for the answers, ko888 and blackmancer!
ko888, when you say "one 6-pin PCI Express supplementary power connector is electrically sufficient" do you mean that I can just not plug the second one in, and the card will run okay? Or should convert the SATA power to PCI-E, as I described with a cable?
I'd like to play Farcry 3 with this system, and I don't want the graphics card to break because I tried to save $70 on a power supply. I'm building exactly
this system but hoping to salvage my old PSU.