If you want the best visual quality + high(er) frame rates at 4K, you’re going to need the best hardware available to run it.
10900k or Ryzen 9 59x0 + RTX 3070 or better or 6800XT/6900XT(when the latter launches), 32-64GB of RAM and at least a 1TB NVMe.
If you’re not willing to fork out much money for top tier hardware, you’re going to have to adjust your expectations when it comes to visual quality and frame rate performance. Either you’ll have to settle for slightly lower visual fidelity or lower frame rates.
That said, higher frame rates are nice, but If you can get 30+ fps consistently, you’re in great shape for a civilian flight sim. It may go well above that in some cases, but if you can keep it above 30, you’re laughing.