Radeon hd 6770 or the 6850?

Hi... I recently purchased a gigabyte radeon 1gb radeon hd 6770 from a nearby Micro Center. When i went in the store i was thinking on not purchasing a graphics card from them because i thought i had decided on purchasing the 6850 from tigerdirect online. It would be great if they could have matched the price of $119 with rebate from tiger direct. After i got all my other parts for the build i was doing. I was talking to an employee and after a while i just decided to go with a $117 dollar gigabyte radeon hd 6770 and got the warranty with it. He said that he plays diablo 3 with that card. I said i was planning on playing that as well (tbh i dont really care). I am also interested in playing skyrim and bf3 maybe at a respectable high or ultra setting. The rest of my rig is 600 watt diablotek power supply, asus m5a78l-m lx plus motherboard, 8gb of ddr3 1333 ram, and fx 4100 quad core 3.2ghz. I actually did not fully put together the rig. I did not take the graphics card out of its packaging. The only thing i actually did with it is open up the box to have a look. I am wondering if i should go back to the store and ask to return it so i can go on tiger direct to buy the 6850. I have seen reviews on the 6850 and it seems like it is a better card. However, i am wondering if i should actually just use the 6770 and try overclocking and see how it preforms with my rig. I know this is very long and I am starting to feel bad that i chose this card. Can someone please show their opinion? Here is a link for the 6850 on tigerdirect http://www.tigerdirect.com/applications/SearchTools/ite...

I am also interested in prepping this comp for the upcoming release of Guild Wars 2