System Wattage with GPU in FULL Stress = 340W (using GTX 780 and six-core Intel Core i7-3960X OC'd at 4.60 GHz on all cores and energy savings disabled). Since you won't/can't OC your i5-6600 (and it's only 65W TDP), power draw at full stress should be lower than 340W shown http://www.guru3d.com/articles-pages/geforce-gtx-780-review,9.html