Ecky :
BigBoomBoom :
Don't forget i7-7700k temp spike issue, Skylake does not have this.
Which issue is this?
Under stock clocks, the processor should behave normally, albeit warmer than skylake.
There are some people who seem to be having issues even at stock clocks, however that is generally regarded as a manufacturing error and should be covered under warranty (at least so far as I have seen)
The issue is the Thermal Interface Material under the heatspreader, which is notably poor this time around.
The solution is simple, delid the processor and replace the thermal paste with something superior like AS5, MX-4, etc.
The downside is that voids the warranty, despite it being very simple to do.
Some people go a step further and replace the material with "liquid metal" thermal interface, which is probably about as good as one can get with a non-soldered heatspreader. But this more extreme than you would likely need to achieve respectable overclocks and temperatures.
For me, the temperature alone would not scare me away from Kaby lake, if it truly was unusable I would warranty it. If it is fine, I would keep it that way until I was satisfied there would be no defects in the chip and I wanted to overclock and delid it.
Skylake does not have this issue but max clock speeds are limited as stated compared to Kabylake, which means it performs very closely to Haswell's 4790k when overclocked.