Well we got already 8 core Broadwell E 6900K overcllocked to 4.2 a bit faster than 4.0 1800x.
Considering skylake 8 core will have even better IPC and better overclockability over Broadwell E ( so more than 4.2 ) it can be quite a bit faster than 1800x. Correct me if im wrong here?
The issues is the base clock. Base clock is basically what a chip guarantees for all cores maxed out. The 10 core is only going to guarantee 3.3Ghz with all 10 cores fully loaded. This platform can obviously be used for gaming but it's supposed to be more about heavy load situations and needing more cores. So in the majority of cases you would want this platform you're looking at using all cores and 3.3Ghz for the 10 core, maybe lower or maybe the same for the 12 core. It's rumoured that the 16 core AMD chips with 20W higher TDP will have base clocks around the same.
If people are making the argument that 7700k is a better gaming chip than the 1700-1800x because you don't need the 8 cores but more clock speed, then similar goes for Skylake-X, for real workstation duty more cores generally wins.
I suspect a 3.3Ghz base 16 core Zen will compare extremely favourably with a 3.1-3.3Ghz base clock 12 core Skylake-x for most of the duties such a platform exists for.
Higher clock speeds for if you want the platform for a mix of gaming and other heavier duty works could easily be in Skylake-x's favour, with higher clocks when not all cores are heavily loaded and it's not at TDP for sure, but how much better and at what price premium will be interesting. It also looks like AMD's platform has a heck of a lot more pci-e natively(though some might be disable or non working and in effect not usable for the 2 socket platform due to lacking pci-e connections).
The Kabylake-x though, is just dumb. If you have enough to go for £200+ mobo and buy into the HEDT platform, you have enough for more than 4 cores, if you are tight on money, then 4 cores on a cheaper platform with Intel or 6-8 cores with Zen is also far preferable. The sole thing Kabylake-x has is tdp. Natively it will boost higher than 7700k because it has what, a 20-25% higher tdp, but who the hell can't overclock their 7700k and get the same thing anyway?
If you want some kind of IO monster station without much CPU grunt, there will be better platforms than HEDT which really isn't making IO monster mobos and that isn't it's market and those quad cores have less pci-e lanes so less options to run lots of extra storage cards. Again for some kind of machine without much CPU power but a hell of a lot of pci-e and potential storage options then something ARM, or proper server or seemingly AMD's IO monster Naples is going to be great.