One HD 5970 consumes up to 240w of power when testing with Crysis Warhead: 1600x1200, FSAA 4x, DirectX 10/Enthusiast, "frost" map. More if you attempt to use FurMark. Therefore, two HD 5970 can potentially use up to 480w of power; but most likely XFire does not scale up 1:1. If I had to guess... about 430w - 450w under typical gaming conditions.