Hey, I have experienced 7200 RPM disk 100MB/s, SSD 500 MB/s read and currently nvme 1,7+ GB/s in last 3 months (DCS 2.5) on Windows 10
From my point of view, SSD 500MB/s is enough. And absolutely must in compare to old RPM discs, if you dont want to spend years before loadings
I did not have same feeling from SSD 500 to NVME 1,7+ upgrade but its of course better.
Im not quite sure that you wont be capped by CPU and RAM. I have upgraded from FX 6350 to Ryzen 7 2700x and this helped very much too. Experience from SSD 500 Mb/s.
Conclusion
If you dont care about the money, go for NVME. If you care and rather spend it elsewhere, dont worry. high S-ATA SSD is enough. But the game is currently quite a big and it will grow so its up to you. But there is high price drop expected in next years. So..