Both the 670 and 680 are lower spec cards compared to the 7970GHz, so if you got the cash, care about benchmarks and want the best go for the 7970GHz.
As far as the latency issues thats a bunch of bull, I can tell you that I get stuttering in some of my games occasionally with my SLI GTX 680 setup so smooth gameplay is just a gimmick that Nvidia is running with
Most seem to forget than once you overclock the Tahiti chips they scale hugely when compared to Kepler. There is no reason to go with Nvidia this round unless you want 3D or need cuda especially with prices today