To answer your question, run this simple test:
Run YOUR games, but lower your resolution and eye candy.
This makes the graphics card loaf a bit.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.
A current gen cpu upgrade will be good regardless.
I would buy the I5-12400 in preference to the I5-11600K
The performance is similar, but the 12400 will cost less.
The 12400 can use any lga1700 motherboard, and there is little value in the more expensive Z motherboards.
B660 works just fine. MATX motherboards will be cheaper if you do not need more than 4 expansion slots.
The 12400 is not overclockable.
Nor would you want to overclock. It turns out that for gaming, performance is better using the turbo mechanism on a few cores than an all core overclock. The 12400 comes with an adequate lga1700 cooler.
FWIW, I am not in favor of the F suffix processors. The extra $20 or so for integrated graphics can be a lifesaver in testing and diagnosing gpu issues. You also get quicksync if that feature is of use to you.
If your time frame is flexible, the 13th gen I5-13400 is due to launch soon.
https://videocardz.com/newz/intel-c...faster-than-i5-12400-in-first-retail-cpu-test
Intel is not much dependent on ram speeds. I would reuse your 2400 speed ddr4 ram.