there's a bit mere to it than that negsun. Nvidia Gpus are faster at folding... even folding project designer said so
source
The 3450 256 isnt exactly a bottom barrel card, yet it folds 100 times slower than the 8800gts. From all i've read on it, The CUDA functionality is the key difference. Of course, it is probably the only thing CUDA is good for ATM
mtfbwya