This is a thread where I have created and validated my own 5950X and 5800X3D same condition benchmark scenarios in the past.
The 5950X and 5800X (not X3D) can be considered nearly equivalent in MSFS, except that the 5950X may generate more heat.
Therefore, the 5800X (NOT X3D) may only be slightly better than the 5950X. (A friend of mine was a 5800X and it is only slightly better than the 5950X)
5950X: 2CCD (8C16T + 32MB L3Cache) x 2
5800X: 1CCD (8C16T + 32MB L3Cache) x 1
The 5800X3D shows a significant performance improvement.
We have not provided a clear percentage improvement, but you can make your own judgment based on the chart.