The 7000 series was made to compete with Nvidia's 600 series GPU's. The HD 7850 surpasses even a GTX 560 Ti in most games and certainly, the GTX 560. Not really a good comparison. I'm an Nvidia guy, but even I know when AMD makes a GPU that's better than Nvidia, I don't let my fanboyism get in the way of my judgement.
http://www.tomshardware.com/reviews/radeon-hd-7870-review-benchmark,3148-6.html