Ive looked at gpu benchmark.com and saw that the order goes 7850>650>6870 , but I'm not sure if those are reliable or not, because the 7850 has only 1 test. Also the 7850 has a lower G2d score, so IM pretty confused. Any input you have would be a big help, since I'm not very expirenced.
I say go for the IceQ X HD 6870. It seems to be the best deal in the way of features and has more reviews on newegg. (66 compared to 3 and 1) Whatever you choose, you may want to wait until black friday, as that's coming up soon.