[juergbi]

M.2 wouldn't be a bottleneck. It supports up to PCIe 3.0 x4 which has a maximum bandwidth of 4 GBps in each direction.

[iotku]

NVMe specifically, as M.2 is just the connector (which can also use the slower SATA interface) rather than the interface.

[Sephr]

Actually PCIe specifically. NVMe improves performance slightly, but it's mostly all due to PCIe.

I have a non-NVMe Samsung AHCI M.2 SSD from 2014 that gives me ~2.3GB/s sequential reads and ~1.2GB/s sequential writes, no NVMe required.