Coming from an intel system into an amd 7700X for a few months, and then to a 7950X3D a week ago, here’s my take on the performance differences and expectations, and why I think we see such a variety of experiences with them…
The Intel cpus and normal AMD ones (especially Intel though) tend to perform much better during constant CPU limited scenarios, intentional or otherwise. Ideally we want the sim to always be slightly GPU limited, but when the CPU demand gets too high in FS they are able to handle that transition to being CPU limited gracefully and they lose performance less dramatically as that load increases. This also means they have higher resilience to large stutters and recover faster from high transient loads, like loading in a massive airport. Their high clock speed lets them burn through those interruptions faster and return to a stable framerate but their lower cache can mean more microstutters near the limit of their performance.
The X3D chips run at a much lower clock speed, so when you overdo it on the TLOD or something really big needs to get loaded, something that takes much more than one frame, and the cache can’t cushion it… they can stutter hard… and they are slower to recover from it. On the flip side though they have a much higher tolerance and throughput on stable high complexity scenery loads due to the vastly increased cache. Consistently dense scenery and photogrammetry performance benefit tremendously from this, and with far fewer or no microstutters.
So it really depends on your general flying situation and needs I think. They’re both great but have different strengths. There is no ‘best’. If you’re always running complex airliners over moderate scenery density and flying into very high detail airports, with a lot of other companion apps running in the background, you may ultimately be better off with a 13900K. If you’re more into extreme visual fidelity though, and lots of low and slow (or low and fast) flying over photogrammetry, and/or VR (where you are concerned with stable framerate and frame time consistency above all) you may find the X3Ds are a better fit. If you play to the X3D processor’s strengths and avoid its weaknesses it can provide a much smoother sim in my experience so far.
The 13900K is very much like a Golf GTI in a way. It’s has really great and predictable handling, and will hold your hand and help you out if you overdo it around a corner. The X3D chips are more like a Lotus. The grip is just ungodly, but if you just slightly overdo it… you’re in the fence. 