I have been trying to decide whether I should get the MSI GTX 680 Lightning 2gb or the MSI GTX 680 Twin Frozr III 4gb. They are both the same price ($600) but I'm not sure if 4gb will really do me any justice. I plan on doing some minor overclocking for now and maybe a 3-4 years down the road, I plan on doing some heavier overclocking to match the cards that will be out by then. As of now my resolution is 1920 x 1080. I don't play skyrim and I don't think I ever will.
Get the MSI Lightning, there is virtually no difference between 2 GB vs 4 GB Vram unless you games at Eyefinity resolution which both card GPU will run out of juice long before you run into memory bottleneck.
Unless you have a personal preference toward Nvidia card, the Gigabyte HD 7970 Ghz edition with 3 GB memory can overclock as high as that MSI Lightning and that extra 1 GB of memory will come in handy later on if you need it for high resolution gaming.
I have had an AMD card and an Nvidia card before. Nvidia's drivers were better at the time plus the card lasted me a lot longer than the AMD card did. If I were to go with an AMD card, it would most likely be the 3gb Lightning.
While it looks like your choices are this 4gb card or a 2gb with a slightly better heatsink and cooling capability. You already mentioned you are going to do light overclocking currently, so I would just grab the 4gb card now, and than OC more down the line. Who knows during that time the 4gb may help you more than the slightly better heatsink will do for your OC which honestly probably won't help much if their both good heatsinks.
So my vote goes to the 4gb card which has more Vram than what you can probably throw at it as of right now as it may end up being more future proof.