It depends on what you are trying to push out in terms of framerate.
I have a 3700X and an RX 6800 XT currently and can push most competitive titles to 240FPS at 1080P. Other titles that are more taxing can vary. I play Warzone 2.0 at pretty respectable frame rates being 100-150FPS as well at 1080P. It really all depends on the titles you want to play, your resolution, and your target frame rate.
At 1080P you will usually be using your CPU more as you will be rendering in as many frames as possible, provided you aren't taxing the GPU with crazy high settings, while 1440P will tax your GPU more, you will still be able to push high frame rates if your GPU is not being over worked.
There is always a limiting factor. The higher the graphical fidelity the more it pushes the GPU. The lower the fidelity and resolution the more it will allow for your CPU to stretch it's legs.
I assume you are asking for gaming information.
In multithreaded workloads the 12 cores of the 3900X will serve you well in most situations.
I personally would look into the benchmarks and times to render of the 3900X if I were looking for specific information. Just because there are other CPUs that exist that can perform better does not mean that a CPU isn't a viable option.
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