You are more likely to upgrade in the future? I got a power supply thats just right for my p.c at the moment, but if I add anything big on like another graphics card I will have to get a higher one.
no? lol, 2 6970s should be fine with a 1000w like the 580s. if not planning to sli or crossfire then a 750w-850w psu should be perfectly fine for breathing room to cover pretty much every area.