I don't really see how the OC/Superclocked versions are that much better. First, you can probably overclock your stock 680 to the speeds that the OC/Superclocked versions run at easily. Second, the OC version doesn't really add much in terms of a performance increase. If you look at benches, usually no more than 5%. I think you'd be hard pressed to even notice a difference in game. I've seen these OC/Superclocked versions as more of a marketing thing to be honest to get more money out of buyers. Just get the version that's out now, you'll be more than happy.
I can see why you'd want a 4gb version if you're running super high res in SLI, but that'd be about it. I think the only game out right now that comes close to taxing the 2gb memory on that card is BF3, I've heard that it uses about 1.8gb in 3monitor mode at ultra. I really don't think 2gb versus 3gb makes any difference now in a year from now unless you're running 3 monitors.