I have two machines, one with an 8800K and one with a 9900 K .
The 8800K has an 1080TI and the 9900K has a RTX 2080 TI.
Both machines are OC to 5.2 GHZ.
I can not make any discernible difference between the two in FPS in a practical sense .
However when I turn off hyperthreading on the 9900K and limit it to 8 cores I can run it at 5.3Ghz and that makes a huge difference.
Moral of the story? MSFS is CPU bound and hardly uses more than 4 cores and still mostly 1 core.
The GPU clearly still makes little or no difference due to the legacy Graphics API in use and the fact MSFS is still CPU Bound.
(Why two machines? I keep one at work for my pleasure.)