shubham_66 is right. I also recommend either a Z77 or Z68 motherboard. They will allow you to overclock, and have support for SLI and Crossfire, which you might use in the future. Also, what games will you play? The 7770 is good, but on Newegg it's $5-10 cheaper than the 6850. The 6850 is a lot more powerful than all of your suggested GPU's, but it will play BF3, Crysis, Skyrim, on Very High or Ultra. In comparison, the 7770 might only play on Medium or High. The 6850 has a lot more longevity.