Thats something thats controversial. The 6800 is more expensive than the 6600GT, thats one thing. Personally, I don't care much about their hardware specs., sorry. But, as for Performance, I believe the 6800 performs better in some situations, and the 6600GT performs better in other situations. If you tell me what kind of games he plays most (I'm guessing FPS) then I could recommend one over the other.