Thing is with the 4GB vs. 2GB is that if you can get 4GB now, why wouldn't you(obviously price, but if you are looking at 2x cards at this stage I'm sure you could push the boat out), might as well at least your going to future proof yourself for little amount of time even if its not "really" needed now,
True, but it's a case of "How long are you going to keep the cards?" verses "How long till the next generation of consoles come out & PC gets a sudden jump in graphics?", If the first is smaller than the second; 2GB, if it's the other way around; 4GB. Admittedly; I'd love to get a pair of 4GB 670's, those would keep my PC ticking over for a very long time, as my 550's are starting to feel the burn in some conditions, plus a single card isn't quite fast enough to run a whole game by it's lonesome in some cases.
Well this is the thing, however, if games now are pushing 2GB now, things are only going to get more ram intensive as games progress, well, unless technology means that they can become more visually stunning and less ram intensive. Man its a hard call.
a 670 4gb is the last thing my rig is calling for. After that upgrades will be out of boredom not necessity
most people here will upgrade again before the next console is out. if you dont game above 1920x1080 rez then 2gb is enough way enough