Adding to Morbad's comments on this bit: when you are CPU-limited, it's not always at 100% CPU utilisation. It is often the case that a multi-threaded game will lean more heavily on one or two of the threads relative to the others. The most extreme/trivial example would be a single-threaded game, where its usage can never exceed 25% on your 4-core CPU.I did a couple hours playing with settings last night and found my CPU is not really hitting 100% much at all, it average below 80% most of the time except in stations. I am still not really sure why and neither the CPU or GPU maxed out, the FPS just drops.... it must be an odyssey thing.
Comparing a 6500 vs 7700K vs 12600 (current CPU, best upgrade in that socket, and a plausible Intel option on a new board) for single thread performance ratings here, you get: 2123 vs 2732 vs 3876.
That's an incredible leap up in single-threaded* performance with the 12th gen relative to what you have now. Even the 7th gen is OK, but I'd agree that even the second-hand pricing for it isn't very attractive in terms of value. My own 7700K can just about handle EDO, but asking it to run OBS at the same time is proving iffy.
(* The multi-threaded improvement is much larger of course, given 4 vs 8 vs 12 execution units.)