9400f and 9600k are the same cpu, except for the ability to OC. Same IPC, same threads, same bandwidth same everything realistically.
You'd be trading Nike tennis shoes for Adidas tennis shoes, thinking that's going to improve your running speed. It really won't. You'd need running shoes instead. Preferably with spikes. That stands a good change of improvement.
You'd need to go higher, 9700k/9900k to see any sort of improvement due to Lcache size, thread count, clock speeds etc and even then the improvement may not be as large as you think or hope, it'll depend entirely on the game code, what it uses, how it's optimized, does it take advantage of stuff.
8 cores is better than 6 cores, only if the software uses it. If the software...