U'd be surprized. In games yeah the memory is very beneficial to the performance, the likes of GTA4 and.. <that war one I can't think of with a built in benchmark, world in conflict maybe>.. have a meter that shows how much ur using. With 1G on a card I can't play GTA4 at max cos.. well there aint enough, even for a 20" screen. But it'd still do a bench run, the graphic requirements ofc are preallocated to the card's memory b4 u execute. It's not a case that the thing will run until it runs out of memory, like ur pc's memory will allow.
It's almost like u change the settings ingame - if it's permitted, u have enough graphic memory - if it won't allow it, u don't.