<p>It depends on how far you plan to OC the GPUs and what other hardware you have in the machine. Each 780Ti in a medium state of tune is going to be pulling up to 300W under maximum load. Each CPU might be pulling about 150, depending on how low you can get the voltages stably. That's 900W just for the GPUs and CPUs. And then there's the motherboard itself.</p> <p>&nbsp;</p> <p>I'd say 1000W is fine with no or minimal OC, but probably quite tight if you start to push beyond that.</p> <p>&nbsp;</p> <p>I use a 1500W PSU in my SR-2 system with 2x 780Ti, 1x 8800GT, 2x X5650@3.33GHz, 13x 3.5" 7200rpm disks and a few other low power bits and pieces (SSDa, various USB paraphernalia, etc.).</p> <p>&nbsp;</p>