6570 is a good buy at 45-50 bucks as well.
lower your resolution to 720 instead of 1080 and the 6570 will game better than xbox
med settings at 720 is better than xbox for sure on but not on ports
mind you the 7750 is going to be night and day but with your PSU i think that may be to high at load
Well the specs says 16A on the 12V, which is 192W. It's also apparently rated at 90% efficiency, although that might be a lie since they don't say it's 80 PLUS certified Platinum. Still, looking at the actual power draw for the 7750 from the chart, 158W from the wall with an i7 3960X is do-able.
If a PSU upgrade is required I'd probably go with one like this:
FSP Group 270W mini ITX 80 PLUS Certified $62http://www.newegg.com/Product/Product.aspx?Item=N82E16817104073