Single core speed is king, unfortunately. If you want to take advantage of performance increase you need a fast single core performance. A CPU with 6 cores at 4,7 Ghz will outperform a CPU with 12 cores and 3,7Ghz. In MSFS you need a fast CPU so the communication between CPU and GPU can flow fast. Then the high end GPU will take advantage of all features. Performance increase rests on combos, not just one part. A 4090 with a slow CPU will idle, that is unfortunately gaming since 2000. Extra cores will not make any difference unless the fastest core is fast.