5.2GHz isn't really very much of an overclock for an
i9-9900KS that has a default Max Turbo Frequency of 5.00 GHz.
But those things have a reputation for running on the hot side even at default frequency..You might wanna check out
this thread and the GamersNexus and Hardware Unboxed videos in posts 31 and 33 about the power and thermals, seems to be a mobo BIOS issue with some boards exceeding Intel specs.
Anyway, 45C-65C during gaming is definately not an issue but with some BIOS tweaking you might get it down..Ambient temp will be a big factor as well as case ventilation, rad fan orientation (should be sucking in outside air), and Vcore at Idle/Load.
My H80i V2 liquid temps were 24C Min/25.4C Max running
Superposition which is a graphics/gaming bench..CPU Cores temp were 22C Min/53C Max.
Running
IBT which is a CPU stress test from hell..Liquid temps were 23.7 Min/28.9 Max..CPU Cores were 22C Min/67C Max.
My ambient about 20C...Temps were taken from Corsair LINK..I uninstalled iCUE because I think it kinda sux and I don't need it just for my cooler..There should be Fan/Pump presets you can choose from or make your own custom curves in iCUE like you can in LINK, I forget.