Just to complete the picture, I pulled the Tesla M2090 and Syba SATA III cards from the Z620 and re-run the tests.
Here are my new Passmark scores;
Passmark System Rating= 4218 / CPU= 19623 / 2D= 571 / 3D = 4623 / Mem =1641 / Disk = 8112
System: 2x 2670, 64GB 1866MHz, 256GB Samsung SM951 (via ASUS Hyper M.2 X4 Mini) boot disk, 480GB SanDisk Ultra II, 2TB 7200rpm, 4TB 5900rpm, Quadro K4200
Using CrystalDiskMark 5 gives the folowing;
So it appears either the Tesla or Syba cards (or both) were reducing the bandwidth of the M.2 SM951 but again, no major increase in boot speed. I expect you need to follow the instructions in the link above to perform a UEFI boot disc to see an real improvement in boot speed. Would be interested to hear from anyone you has performed the clean install as listed in post (specifically on a Z620) above and if they notice any real improvement in performance.