Although people may call the 9700k/9900k just rebranded Coffeelake, there are clear improvements over the i7-8700k.
People are right when they say intel should have always refrained from using the pigeon poop TIM under the IHS, but even with this paste, it was and still is a clear winner for IPC vs IPC, stock clocks vs stock clocks and OC potential vs OC potential against absolutely anything AMD has to offer and that also applies prior to any delidding.
Even with the Thermal limitations of the poor TIM, the i7-8700k comes out on top in all these specific tests in pretty much any benchmark you'll find on the web. The positive differences we have this time around is that rather than the need for delidding to push the boundaries and to try to achieve that 5ghz or greater OC, we now have a soldered IHS that will significantly lower thermal limitations and we also have an Intel 8 core 16 thread mainstream cpu that is capable of 5ghz out of the box, no OC, delidding or special requirements needed, it will hit 5ghz over 2 cores without touching a single bios setting.
When you think that an 8 core 16 thread cpu with a higher IPC will go 5ghz out of the box, there is no reason for anyone to suggest that it wont take some serious beating. This 5ghz is also a very reserved and a very safe turbo boost that is designed for people to run these clocks under the poorest of coolers, making sure that they keep their RMAs down to a minimum.
I personally feel i'm not going to be too far away when i suggest that we will be probably be looking at a 5.2ghz chip over all 8 cores with 16 threads for the I9-9900k (when under decent cooling of course). The 8700k had a max boost of 4.7ghz but has an average overclock of around 5ghz with some cases higher OC over all 6 available cores, this means it had a 300mhz overclock boost over its max turbo clock on all cores, if you had a 300mhz boost on top of the i9-9900k's max boost over all of its available cores, then we'd be at 5.3ghz.
You could even say 5.2ghz is being reserved what with a now soldered IHS and refinements to 14nm++....This I9 is going to be one hell of a fast cpu and surely nobody can deny this?
I personally think you could subtract the small performance percentage hits of any windows 10 patch/update/code for as many security flaws as you wish, there still wont be anything come remotely close to it in terms of actual speed.