I've just ordered a BTO 20 inch iMac but now, being a gamer i feel that the GPU (256 VRAM X1600) isn't gonna last down the road. My first question is whether the GPU could last 2-3 years? Next i was wondering about returning it to apple in exchange for the 24 incher with the 7600 GT. I've heard things like such an exchange is not possible since my 20 incher is a BTO. So, i cant exchange it even if i'm willing to fork out the extra cash for the 24 inch iMac?