I'm not trying to change your mind, and correct me if I'm wrong, but I've always found the ATI cards run better with AMD processors, and nvidia with intel, maybe its the company or something(?). Anyway I agree with ROck, 7950 is very good, if not a little expensive. But it's always best to buy the latest, as it lasts longer. But the 6970 is cost effective and will probs do the job.
AMD GPU's do not run better with AMD processors, you will get more performance (by far) with a 2500k + 7970 than a 8150 + 7970.