It wouldn't have that much impact no I wouldn't presume.
It'd help more for multitasking and caching of programs and some data. Your video card won't use much of that ram for caching because the max you can set it to is 512mb and as the game is concerned, no.
It's just like a new CPU, it doesn't boost it half as much as you'd think.
The graphics RAM is what matters but this wouldn't help fps much, and only for textures and high resolutions which might help a bit...