Just another piece of information regarding the UEFI boot install;
After completing the UEFI boot install on the SM951, (and re-installing my SanDisk SSD and 2off HDD's I removed before the installation), it is now possible to switch booting from either the SM951 PCIe drive or the SanDisk 480GB SSD, (which had my OS and programs already installed). When you go into the BIOS it is possible to disable the Windows Boot Manager which forces the Z620 to boot from the SanDisk SSD OS drive. Everything is back as it was before the UEFI installation.
To boot from the SM951, you simply re-enable the Windows Boot Manager in the BIOS.
Although it's not required, I would recommend you disable the other OS drive when re-booting from the SM951 otherwise you will see 2 additional drives in Windows Explorer, (a System Reserved drive and a Local Disk drive). FYI, the SM951 is GPT and the SanDisk SSD is MBR.
If you decide not to disable the original MBR OS drive in BIOS when booting from the SM951, you can copy files from your old User folder to the new GPT OS drive easily. (Note: May not work if you re-install with a different user name due to permissions but not 100% certain).