If it were me, my choice would either be between the 7850 or the 670. The 7870 is ~$100 more than the 7850 but not worth that much more for the performance increase imo, but the $150 increase for the performance of the 670 is.
Yeah, saddly for me 400$ in a GPU it's just too much. Or maybe if I can save something changing some pieces of my build I can go for the GTX670. I have to check that. Thanks for your answer.