TBF you'd have to be doing some heavy video editing before the X99 becomes worthwhile. If you're just doing the odd couple of hours in a week, then I doubt the increase in performance will be worth the spend. That's why I went for Z170 with my build.
It's not so much the chipsets are different rather than the fact they're both separate sockets. X99 is LGA2011-3 and Z170 is LGA1151. The former is enthusiast range whilst the latter is consumer range.
Basically, it depends on what work you're doing. If you're doing 3D rendering, animation, VMs, video editing and so forth, the X99 platform is for you since those sort of applications take advantage of the extra cores.
If you're primarily gaming or doing some limited work on the side, it's in your best interest to go for the cheaper Z170 socket. By the time games utilise all cores, both sockets will be irrelevant.
