I say give a 4670 so you can get some AA turned on.
I had a 3870 and it was ok but any AA and my FPS dropped alot
Also I would stay away from buyying computer parts on ebay
Look at this one.http://www.newegg.com/Product/Product.aspx?Item=N82E16814161249
It has the IceQ cooler so hot air goes out of the case. And you dont need any 6 pin Power plugs.