Graphics cards are rapidly dropping in power consumption. The most expensive GTX 680 only recommends a 550W PSU. Today 650W is overkill for a motherboard that only handles one graphics card. I wouldnt go above 550W unless the price was the same (which sometimes happens).
Well I factored in, that when my 660ti get's old I would eventually want to upgrade and need a higher psu so I figured a good 650watt will do.
One other thing - The Rosewill Challenger case is not terribly wide for a gaming case. A 120mm cooler like the Hyper212 or Gaia might not fit. The coolermaster HAF 912 and Antec 300 are similarly priced and wider to handle 120mm coolers. The HAF 912 would be my recommendation for a case right now as its on sale.