they are pretty similar in performance http://www.techpowerup.com/reviews/HIS/HD_7750_IceQ_X/11.htmlhttp://www.techpowerup.com/reviews/HIS/HD_7750_IceQ_X/22.html
the 650 has a slight edge, and its cheaper. so i would get that. If you are planning at maxing games out at 1080p then forget about it. You need to spend a lot more money, something like a gtx670 or 660ti.