k.my friend has a 896mb gtx 260 but while playing gta 4 he says that he cant increase the graphic settings as it crosses 896 mb while on his other desktop where he has 1792 mb version he can increase the settings to highest
on 1792 version gta 4 shows
1000mb used/896 on core 216 edition
I've seen quite a few articles and posts from people saying that GTA4 is almost unplayable on a dual core so if it likes cores, real or virtual, then the i7 is going to win the fight, and the drivers are Nvidia ones and as such unlikely to be the problem.
Interesting you should say that considering the arguing that was going on over in the CPU forum about that.
@OP Try swapping the cards over, see if the frame rates follow the card or stay with the respective rigs as it'll take ten minutes and give you a definite answer. It may well be the extra Vram or it might be the CPU.