Theres basically nothing that can run X-Plane well at higher settings, especially in bigger aircraft. Your best bet is a overclocked high end Intel consumer CPU.
I think that says more about Austin Meyer's insane hacker mentality than X-Plane's deficiencies. Of course he'd allow setting maximum detail/frame levels that are far above what modern desktop machines can deliver -- maybe someone with a 64-core Xeon and paired top-end NVIDIA cards wants to max out such a system :)
More than 4 cores doesn't help with the current engine - that 64 core Xeon is going to be clocked lower than a 9700k and perform worse. You could run 16 instances but none are going to run faster.
Is X-Plane suffering? As far as I know, it's the only consumer flight sim that does rigorous physics calculations -- https://www.x-plane.com/desktop/how-x-plane-works/
Or did you mean rigorous simulation of plane systems, ATC, ILS/vectoring, etc.?