Below are the lowest priced HD 7770 (GHz Edition = Stockspeed) and GTX 650 Ti @ stock speed of 925MHz. Based on the chart above the stock speed version of the GTX 650 Ti has 96% of the OC'ed version @ 1072MHz. That means the Radeon HD 7770 GHz Edition has about 74% of the overall performance of the GTX 650 Ti @ stock speed. Another way of stating that is the GTX 650 Ti has 135% the performance of the Radeon HD 7770, or simply it is 35% faster.
Based on the after rebate prices below and including shipping the Radeon HD 7770 costs $85. The GTX 650 Ti costs $90. While the GTX 650 Ti costs about 6% more, it also provides about 35% more performance. That makes the GTX 650 Ti the best bang for the buck.
Radeon HD 7770 - $80 after rebate +...