If you have a Ryzen CPU it will make a bigger difference than an Intel, but it will still be pretty minimal.
This is untrue. His i9-9900k is actually quite close to i7-10700k especially when overclocked to 5ghz. The i7 is beating AMD latest CPU in this game, see thread: AMD 5900X/5950X Performance in MSFS
Maybe he can gain 10% by overclocking.
About my 2700X, it will never be within a couple of % of the i9-9900k no matter how much I overclock it in this title. The i7-10700k is already over 40% faster at stock speed, I won’t kid myself.