This gives you a pretty good comparison between the cards (at stock):
http://www.anandtech.com/bench/product/1332?vs=1038
Shows the 280 ahead in the majority of games, Crysis 3 & Bioshock Infinite are the two exceptions where the 760 does better. For the rest of the games tested, 280 is better, sometimes only a little, sometimes fairly significantly (30% or even more).