Unless you have a fair amount running in the background at the same time you're playing the game then system RAM shouldn't be a big factor, few games are even going to touch 2GB of system memory leaving 2GB left over. And if need be much of the memory used by those background tasks can be shuffled off to allocate more for the game... which will be a hassle when you want to go back to those applications but that's another matter.
I'm pretty dubious even 3GB of system memory wouldn't be perfectly adequate for gaming.
Insufficient VRAM can really hit performance hard though, the vast majority of games should be able to run maxed out at 1920x1080 with 1GB though (assuming sufficient GPU power of course) so you probably don't need to worry about a 1GB card.
Still, there are some games that would appreciate the extra memory. I know Total War: Shogun 2 loves VRAM, it'll happily use a decent amount more then 1GB.