Not really...the so-called "faster on average", according to anandtech, the 7870 is like 4fps faster in Metro2033, 1fps faster in Skyrim, and in Shogun 2 with the same frame rate and in Civ5 with 10fps ahead, however in Batman the 660 is 4fps ahead, Starcraft II 24fps ahead, BF3 8fps ahead . So it is the case or win some lose some on both cards. However if BF3 is the main game, and not playing older games like Metro2033 and Civ5, the GTX660 is no-brainer really for the newer titles.
http://www.anandtech.com/show/6276/nvidia-geforce-gtx-660-review-gk106-rounds-out-the-kepler-family
What about both the 660/7870 overclocked?. I'm only asking as this forum is usually filled with people who would do so.