The first one is the "SuperClocked 4GB model". The base clock speed is OC'd to 1111MHz.
http://www.amazon.com/EVGA-Superclocked-Dual-Link-Graph...
The Second one is the "For The Win (FTW)" Edition. Same 4GB memory but a OC'd clock speed of 1137MHz. The theory is the FTW units are supposed to be tested better or something. Not worth the extra $40 in my mind.
http://www.amazon.com/EVGA-GeForce-DisplayPort-Graphics...
I'd go with the less expensive model myself. I originally bought the 2GB SuperClocked EVGA ACX when they first released. Awesome card. The 4GB version you're looking at would be good if you're considering playing modded games. For example, Skyrim CAN max out 2GB Video RAM if you run a lot of graphic mods.