I would imagine the same as it has been. The 6700k is the 4c/8t mainstream desktop cpu like the 4790k was and the 6800k is the lower clocked 6c/12t enthusiast or workstation cpu for the broadwell-e platform. Games are still not overly threaded, a couple are starting to make use and show a slight performance improvement with hyperthreaded cpu's but for the vast majority there's not much difference between the i5's and 4c i7's.
X99 is the predecessor to broadwell-e and the 5820k is the predecessor to the i7 6800k you mentioned. All 3 of those use ddr4 and ddr4 shows little to no improvement over ddr3 especially in gaming. If considering 3 cpu's that all use ddr4 though there's really no point in being concerned over how ddr3 stacks up.
There's no such thing as future proof. If that were the case the 8 core fx cpu's would be topping the gaming performance charts and instead they're in the lower half. Often times losing out to an i5 which has strictly 4c/4t or tying with the i3 many times which is only a dual core with ht. Not often but in a number of games the i3, i5 and i7 all perform within a few fps of each other.
Unless this is a video editing rig or you're looking to run obs or twitch or something along with your gaming at the same time the 6c/12t cpu's are liable to be overkill.