I suspect the answer here lies beyond the simple statistic that a singular metric like average FPS will capture and convey.
Take the
techreport's methodology of capturing and reporting the average frame rate for just the 99th percentile, or the time spent rendering frames that exceed 33.3ms.
These are ways to analytically capture and analyze game response factors that matter to the end-user above and beyond a flat "what is my average framerate?" because average fps does not speak to stuttering and lag in ways that the experiential result does.
I have no doubt that a hexcore is unlikely to improve on the gameplay from a flat average framerate perspective over that of a quad, but I have every expectation that a user playing a game on a hexcore is more likely to find the gameplay more fluid with less noticable random minimums in the framerate and so forth.
In many ways this is no different than what Anand uncovered and highlighted years ago regarding SSDs and the lockups they would do with random read/write of small files and so forth. That was a very real issue that was not captured by benchmarks designed to measure sequential bandwidth with large files.
For all the reasons that mattered for SSD users, I expect the same to manifest with gamers and their video cards versus cpu core count (since core count reduces contention on the backend where system processes are transpiring simultaneously).