PC Gamer 9700K review.
https://www.pcgamer.com/intel-core-i7-9700k-review/
At stock, the 9700K is about one percent slower than the 9900K, and overclocked the difference is splitting hairs. The 9700K even claims a few wins, and with a margin of error of 1-2 percent in most games, there's no need to worry about gaming performance.
Relative to the Core i7-8700K, the loss of Hyper-Threading is more than offset by the additional CPU cores. Core i7-9700K is a few percent faster than the 8700K, and a bit more than 10 percent faster than the 2700X. It costs the same as the former, and about $100 more than the latter once you factor in the price of a cooler. But if you're building a primarily gaming PC, I'd still go with one of Intel's CPUs.
https://www.pcgamer.com/intel-core-i7-9700k-review/