I have a VF700 on my 7800GT....and I HATE it....its loud on 12v, but on 5v mode, it doesn't do enough....get something like the new Accelero X1 (from Arctic Cooling...I should be getting 1 monday, I'll post how it does)
But the stock cooler looks to be decent from all I've seen (the new 7900 series runs hot from the reviews I read....6800 all over again?)