When I updated my system a few months back I decided to opt to getting a 500Gb NVMe drive for the OS and a couple of 1TB NVMe drives, one for MSFS and XP11 and the other really for games in general. I also have a couple of SSDs - not at my PC but one has P3D on it I believe and the other is currently empty. I also have another 2TB hybrid drive which is really there for files etc.
I used have P3D on a hybrid drive and as you can imagine it now loads up a flight noticeably quicker. I believe I had XP11 on a SSD before, I think it may load slightly quicker now it’s on a NVMe but it is no where near as noticeable as going from a hybrid to SSD.
My thought process was really to lessen the potential for reading files from a drive as being a possible factor with respect to stutters. As I had also upgraded from a 6700k to a 10900k with faster memory I would say it unlikely I could know if the difference between SSD and NvMe really provides any significant boost in this respect.
If I am honest I suspect there are a whole host of other limiting factors that will more likely cause stutters than the potential benefits of NvMe over SSD might actually provide. Just an opinion though, nothing to offer with regards to numbers!