Before Ryzen 5000 showed up, the 10900K did deliver the best gaming performance - out of the box.
Overclocking isn't worth it on this cpu; getting around to stress testing for OC stability... like, it just pulls too much power. You're not going to pull that kind of power in game, but stress testing is still necessary for obvious reasons, but - I'm going to go in circles here...
I see it like this:
A)Stuck on Intel, want the best overall out of the box gaming performance they offer without overclocking/won't overclock? 10900K.
Then it also has the exclusive Thermal Velocity Boost, which is a temperature sensitive, auto boost feature, that is active up until 70C. This further reduces the need to OC it, as the cpu will try to boost higher on its own, as long as it stays below 70C.
B)Stuck on Intel, want a good overall gaming cpu and be able to play with some OC'ing without donating an organ for exotic cooling? 10600K.
A 240mm hybrid and high end air coolers would suffice for this cpu, including some OC headroom.
AMD has an edge over Intel's best in that they don't require as extreme cooling solutions, allowing users to save some money, or allocate it elsewhere.
A 5900X under loads doesn't even exceed 200w, landing around the 10600K's level of power consumption.
Cooling on a 10900K? Just about any 360mm performance hybrid cooler from a well known brand:
Arctic Liquid Freezer 2, Cooler Master ML360R, Corsair H150i Pro XT... avoid models advertised for low noise operation - they give up too much fan strength, which limits their performance!
^That's including OC'ing.
Without that, a 280mm hybrid, or some of the top air coolers:
Deepcool Assassin 3, Noctua NH-D15S(now available in Chromax Black), Thermalright Le Grand Macho RT...