I was just in your shoes.
I ended up going with the GTX 680 4GB w/ Backplate.
I only game at 1080p right now, but I do like to plan for future expandability. My rig is setup for SLI, so down the road if I grab another card I get to use the power of 2x 680's with a 4GB memory cap since SLI doesn't combine memory.
I also mess with user-made graphics mods for games like Skyrim, Crysis, etc from time to time, and some of those can dramatically raise memory use.