While the 9700K does have an edge in performance at the moment in some games, as newer games learn to take advantage of the extra threads, and games further optimize themselves for Zen2 and AMD in general, the 3700X will become better as the platform ages. Also LGA1151 has been around for a while now, so if you go with the 9700K, there is not telling how long your motherboard and platform will be relevant for. While on the other hand, with Zen2 and x570, you're getting a brand new platform that will be around for a while, and PCI-E 4.0. Both of which will be relevant for a while now.