I'd be looking more in the 1000W range for the 295x2. Something like the EVGA G2 1000w. It's overkill, but it's what I'd do. That card's TDP is only (lol) 500W, cpu somewhere around 100w (depending on your CPU), rest of system 100w, add 100-150 for overhead and you're at 800-850W. so you could get away with less if you really wanted to.