Question about Intel Core i9-9900K

I switched from a 3770K to the 9900K and hardly noticed anything when gaming. Windows 11 will also run on the 7700K. Better wait for the release and test it then before you spend your money on the components now. If your games are graphics-intensive and you play on a 1440p+ screen, then your graphics card will be the bottleneck.

The upgrade has been worthwhile for a long time. If you are explicitly asking for this upgrade because the ulterior motive is to replace the CPU and keep the motherboard, that is not possible. The socket is the same, but the 9900K (generally the 8000 and 9000 CPUs) does not run on Z170/Z270 motherboards.