There has been a bit of confusion about upcoming Intel 6-core Coffee Lake being compatible with the current motherboards like thr Z270 series. Coffee lake makes use of the same socket and as such people expected (or had hoped for that).

It is now confirmed that you cannot use Coffee Lake on existing motherboards. In Specific it was ASRock who unraveled this mystery with a tweet: 
 

As to why Coffee Lake cannot be used on Z270 remains a mystery though. The new processors will likele be introduced in late August or September  with their accompanying Z370-chipset. 

The presumable i7 8700K will have a 95W TDP, 3.7 GHz base clock, 4 GHz boost for 4/6 cores, 4.2 GHz for dual core and 4.3 GHz for a single core (likely 2 threads). Then there will be a 95W part with 3.2 GHz base clock and 3.4 GHz boost for 4/6 cores, and 3.6 GHz boost for 1 or two 2 threads. The last SKU is a 65W chip with a base clock of 3.1 GHz but 4/6 core turbos to 3.9 GHz. Dual core boost is 4.1 GHz while single core goes up to 4.2 GHz:

Coffee Lake Processors will not be compatible with Series 200 Chipsets