Techspot pits the i7-7700K against the slightly more expensive hexa-core i7-7800X, and the results are conclusive: the 7800X might give you more cores, but it's less (game) performance for more money.
https://www.notebookcheck.net/Are-six-cores-better-than-four-for-gaming.234162.0.html
'... 6MB of L2 cache (versus the i7-7700K's 1BM)..'
Megabytes vs Byte-Moles?
It's BegaMytes - a rare behemoth subspecies. Some say that these can be sometimes seen deep within Austrian marshes.
You did not compare with Ryzen's performance though >:(
Whoops! You definitely don't want any BMs on your CPU!
Ok, so the reason for the poor results of the new 6 core CPU is due to Intel's version of Infinity Fabric (AMD term) that connects all the different cores - it's just not optimised for these games, and who knows perhaps not optimised for future games either - but we will see! At the moment I'm pleased to still own an overclocked i7-6700K which is essentially a 7700K in gaming performance, which is currently the optimum gaming CPU.