Note that most/all of the current M.2 SSDs are running as AHCI devices, not NVMe. There's an OEM Samsung NVMe unit not available for retail yet. Apparently the performance difference between the AHCI and NVMe version isn't big, anyway.
Edit: here's the key line regarding a modest improvement for small random access:
> Typically the NVMe version offers about 10-20% improvement in average latency over the AHCI version, which is a healthy boost in performance given that the two utilize identical hardware.
Reference: http://anandtech.com/show/9396/samsung-sm951-nvme-256gb-pcie...
Edit: here's the key line regarding a modest improvement for small random access:
> Typically the NVMe version offers about 10-20% improvement in average latency over the AHCI version, which is a healthy boost in performance given that the two utilize identical hardware.