i have a 5850 and 5830 the fan on the 5850 is an 80mm.when the fan does go i plan on getting something like this http://www.newegg.com/Product/Product.aspx?Item=N82E16835103071 and cut the fan out of the frame,bend the legs and drill the 3 holes.probably have to change the connector,but as long as the amperage is the same it should work
I've done this. You may wish to use a 15mm instead of the standard 25mm depth fan. I used a 25mm and the cooler cover sits a bit high. I just run the new 80mm off a molex.
Also, try and find a fan with a high static pressure spec, since you're trying to push air thru some resistance (of the gpu cooler).
