I think exactly what we are seeing is nvidia laying off Kepler optimizations in new games to push Maxwell sales on existing Kepler owners. If you look at the performance hierarchy in games prior to Maxwell's release between Kepler cards, Maxwell cards and Radeons - 980>780ti>970=Titan>290X>290 it is not the same as what you see in games that have been released since Maxwell came out.
Also, if you go go back and check graphics rich, high tech games that released prior to Maxwell, such as BF4, Crysis 3, Metro LL etc - the performance hierarchy is consistent with what we saw at Maxwell's launch as I laid out earlier. I am seeing this comparing a 970 to one of my 780ti cards. So, we're not seeing across the board Maxwell optimizations, but better optimization in recent games. Also worth noting the games that are showing this most strongly, Far Cry 4, AC: Unity & The Crew, are all Gameworks titles where nvidia can much more easily manipulate performance on their cards and AMD's with their closed Gameworks libraries.
Not really surprising, but not worth biting on still even with driver performance optimization games being played. Release the real high end card in GM210. My guess is partly they are not seeing the usual adoption from 780ti/Titan buyers you normally see with a new flagship launch because the performance improvement between those cards and 980 was pathetic at launch. So forgo Kepler optimizations in games as they release which will show up in review benchmarks to try and push those sales is a good strategy.