what is the best varient of the 7970 i can get for around 500 dollars
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150586
I'd wager the 7970 GHz from Gigabyte's WindForce series. Massive heatsink, 3 copper heatpipes, 3 fans, $450. Hard to argue that. Only con that I can think of is that it's ugly, but shouldn't matter much unless your case has a rather large side windows and you care about that sort of thing.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125439