Indeed, kicks both the 590 and 6990 in the ass!
So add another 400w for another Mars II for 900w max system consumption. Oh but we want TWO overclocked 3930X's in there, so toss in an extra 150w for both? Psshhh 1200w, maybe 1300w tops. Another 80-100w for WC pumps, HDD's, RAM, etc. A 1500w will do, you don't need another damn PSU :PMeasured power consumption one card
System in IDLE = 182W
System Wattage with GPU in FULL Stress = 562W
Difference (GPU load) = 380W