I fly with all settings on ultra and terrain LOD at 200, object LOD at 100. Performance is great, however I want to know if upgrading any of my hardware is going to make it easier to have AI traffic with these settings, especially at big airports. Would an i9-13900K and/or an RTX 400 series graphics card give performance with AI traffic a boost?
It’s better practice, but this will do nothing for performance gains.
You will be limited by your current processor if you want to significantly increase AI traffic. High AI traffic settings put a significant load on the mainthread, and you will be quickly mainthread limited with a 10900K. If I were you, I would invest in upgrading your processor over upgrading your current 3090 Ti. This will allow you to increase the AI traffic settings and/or increase the terrain LOD beyond 200 if you want. Your current 3090 Ti is more than capable of running MSFS.
Unless you can sell yours for a decent price and pick up a very cheap 11900 then you should upgrade mobo and grab that 13900K … only then can you decide if a 3090Ti is enough.