if you run out of vRAM your system does take from system RAM. Performance when doing that is terrible though since higher end gDDR3 might be able to transfer around 50GB/s - 100GB/s depending on the system's memory configuration, while system RAM might be pushing, intel side 6GB/s and that's SHARED with the CPU. most games don't use more than 300-400mb or so right now however, but it does depend on the resolution and settings you're playing at. the big thing which uses frame buffer would be textures, high resolution textures take up a lot of space. That's why if you look at xbox and PS3 games all the textures look relatively cruddy since they only have ~256mb vRAM. again with stuff like this it's about finding some solid bench marking sites and going off of those. the 9600GT512, the 8800GT 256, 8800GTS 640, and 8800GS 384, and 9600GSO are all basically equal in performance it's just that the 8800GS is the cheapest.
Oh wow I didn't realize that. Good to know. I just figured because the transfer speeds were so different it wouldn't actually work.
