Speaking to your RAM question, keep this in mind. Video card RAM becomes more important as resolution scales up. This is because the framebuffer (multiple copies, really, when you consider Z,W,etc buffering that is omnipresent in today's games) is stored there also, and the bigger the monitor, the bigger these buffers.

This is why you'll notice most enthusiasts recommend a gtx over the new gt/gts cards (768M) for say a dell 30" monitor.