If it's a stock PCB this is a brilliant cooler, but be aware it's very large, taking up the best part of three slots!http://www.newegg.com/Product/Product.aspx?Item=N82E16835118061
I have one on my HD5850 and even at minimum speed keeps the card under 50C at stock clocks running the Furmark extreme burn test @1920x1200. Also note, I'm in England and it's not as warm here
so expect higher temps than mine.
As has been said, if you change the cooler you'll lose the warranty and if you've registered the card for that lovely double lifetimer I'd say leave well alone, XFX are pretty good with the customer support stuff.