Personal and anecdotal I’m afraid! When I moved my largest Kontakt libraries from a 7200rpm disk (~110 MByte/s) to SSD (~550 MByte/s) they did not load 5 times faster. Faster, yes, but not 5 or even 4 times faster. I’m planning to fit an M.2 NVMe and I read a detailed test which indicated something similar re. SSD->NVMe but I can’t for the life of me find it now, apologies.
Be aware that there are both NVMe (fast) and SATA (slower) M.2s out there so if you already have SATA SSDs (2.5" form factor) then only moving to NVMe makes sense, but they are orders of magnitude faster.