The 8700K runs at 4.3Ghz all cores, provided the cooling is good enough, given that all reviewers use £150 of higher priced coolers when reviewing the chip what you see in all reviews is best case, some of those reviews on Asus boards the CPU is running at 4.7Ghz all cores.
4.3Ghz is not a low clock speed, pretty much all 8700K overclock to 4.8Ghz with good cooling, that's about a 10% overclock, not much more than what Ryzen 2 overclocks.
Actually this has just reminded me of something, i think it was Guru3D who reviewed a Mideon 8700K Desktop, it had more ordinary air cooling on it, the performance on that 8700K machiene was 10 to 15% less than review samples with their £150+ coolers.