The Tech Report addresses two questions about Intel's i7-8700K in their latest review, how to keep it running cool and how the multi-core enhancement feature changes that answer.  Multi-core enhancement is a BIOS level overclocking feature which allows all cores on Coffee Lake processors to hit the full boost clock instead of only a single core.  In this example, a single core could hit 4.7 GHz while the other cores are being limited to 4.3GHz, however with multi-core enhancement enabled that limit is removed and all cores can hit 4.7GHz simultaneously.  As with any type of overclock this produces significantly more heat and requires more cooling.

This enhancement means there are two answers to the question about cooling your Coffee.  With the enhancement feature disabled you should be just fine with a CM Hyper 212 Evo or equivalent heatsink, however with MCE enabled even a Corsair H115i shows a 90° C package temperature with core temps between 84-90C.  Keep this in mind when shopping for parts; it is nice to have all cores running at their full Boost Clock but you will need to be able to cool them or else see throttling as the chip sense Tjunction temps in excess of 100C.

"Intel's Core i7-8700K proved an exceptionally well-rounded chip in our testing, but the company's choice of thermal interface material has left many wondering whether the Coffee Lake flagship will prove a challenge to keep cool. We establish a handy baseline for what might make a chip "difficult" to cool and see whether the Core i7-8700K falls on the wrong side of the line."

Here are some more Processor articles from around the web:

Processors