Intel's HEDT family so far (Gulftown, Sandy Bridge-E, Ivy Bridge-E, Haswell-E, Broadwell-E)(from 32nm to 14nm):Skylake-X is manufactured on the same high frequency 14nm + process as Kabylake. I'd be surprised if top bins didn't hit 4.6 GHz fairly easily.
Coffeelake will have a six core max (not 8).
3.33/3,60 GHz 3.30/3.90 GHz 3.60/4.00 GHz 3.00/3.50 GHz 3.00/3.50 GHz
If they can hit 4.6GHz, it will be quite a nice leap.