Get a HD7970 and a arctic accelero hybrid and overclock the card.
The hd7970 is a fast cad itself and overclocking would make it turn to a beast. Or you can just buy the card now and get the cooler at some point later on.
The GTX 680 & 7970 GHz have precisely the same performance, so it comes down to wich team you prefer. These are the best single-GPU cards that currently exist and are a little overkill for 1080p gaming (if that is indeed you resolution ?), but very futureproof.