A 760 or 7950 would do the job just fine, the 7950 allowing for more overclocks than the former. You don't necessarily need to go the extra mile for a 680/7970. However, if you would like to, then I recommend the 7970; 50% more VRAM, as well as a 384-bit bus compared to 256-bit.
Plus, now that the micro-stuttering issues have been fixed, you could always buy a second one for SLI when the time comes.