that have nothing todo with that… There is just no big real benefit of all that advertinsing numbers ( like the frequencies in RAM ). On the paper the numbers looks great, but in real it have not the same ‘double it’ effect, also because “MB per Sec” is not all what count and often there is a big portion of advertising included ( how many seconds can the controller work in that speed, caches, read/write/ , etc. ). So, I not expect really a relevant difference. Additional a huge part of startup msfs seems the update check, etc… I remember similar discussions in other game forums for e.g. the 970 EVO vs 980 pro , where users also not noticed any kind of difference ( and not a simulator ).
In my former PC I had MSFS data on a SATA SSD. In the new PC it is one a 980pro nvme , and the loading time of msfs is nearly the same ( I not count the seconds 
).
If we check e.g the taskmanager, we see a short-time high read-rate, and thats it. I buy the “pro” variants for drives which are important or where I expect that more data are written ( the pro’s have usually more warrenty ) or also where I expect that huge files needs to be transfered ( my video projects ). For all others I still have “old” SATA SSDs and not care about that the game possible loaded 2 seconds slower
Also lots of gameing magazines reported about that facts…
here a compare of loading time SATA vs pci3 vs pci4
source: Samsung SSD 980 Pro im Test - Extrem schnell, aber (noch) unnötig
There are tons of other magazines, man yof the youtube guru-advertising-influencer videos, etc. about that 