Most games are graphics limited and not so much cpu limited.
Your difficulty with settings suggests a gpu limitation.
Unfortunately, buying a good graphics card upgrade today is difficult.
3080 cards are unobtainable, let alone at anything less than 2x MSRP.
Many ask about the cpu vs. gpu upgrade question.
My stock approach to this perennial question:
Some games are graphics limited like fast action shooters.
Others are cpu core speed limited like strategy, sims, and mmo.
Multiplayer tends to like many threads.
You need to find out which.
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To help clarify your CPU/GPU options, run these two tests:
a) 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.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 30% improvement in core speed might do.
You should also experiment with removing one or more cores/threads. You can do this in the windows msconfig boot advanced options option.
You will need to reboot for the change to take effect. Set the number of threads to less than you have.
This will tell you how sensitive your games are to the benefits of many threads.
If you see little difference, your game does not need all the threads you have.
It is possible that both tests are positive, indicating that you have a well balanced system,
and both cpu and gpu need to be upgraded to get better gaming FPS.
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If you need to go down the cpu upgrade route, you have many good options.
Any modern processor upgrade is going to need a motherboard change also.
The 11th gen intel processors(and ryzen 5000 series) have improved performance per clock of some 19%
I would not go older gen.
As a base, your I7-6700K has 8 threads and a passmark rating of 8977.
That is when all 8 threads are fully utilized. If your games are multiplayer with many participants, that is most important.
For most other games, the single thread rating of 2532 is more relevant.
If your budget permits a i9-10900k, then you are better off as a gamer with a i9-11900k,
16 threads and a rating of 28082 with a single thread rating of 3764.
Here is a review:
The Intel Core i9-11900K is the company's Rocket Lake flagship. It uses the new Cypress Cove architecture and includes support for new instruction sets like AVX512 and DLBoost to speed up AI calculations. We run the processor through our new test suite and also take a closer look at gaming...
www.techpowerup.com
You will need a good Z590 based motherboard and a good cooler to get the most turbo uptick with the processor.