I'll clear up some misinformation here. This is for UEFI BIOSes without native NVMe support such as most X79 boards.
 
CSM Disabled
PCIe AHCI: Bootable
PCIe NVMe: Not bootable
PCIe NVMe (with built-in OPROM): Not bootable
 
CSM Enabled (Everything set to UEFI Only)
PCIe AHCI: Bootable
PCIe NVMe: Not bootable
PCIe NVMe (with built-in OPROM): Bootable
 
SSD Models
PCIe AHCI:
Samsung SM951 (AHCI version)
 
PCIe NVMe:
Samsung SM951 (NVMe version)
 
PCIe NVMe (with built-in OPROM):
Samsung 950 Pro
Intel 750 Series
 
On X79 you can only boot from NVMe devices with a built-in OPROM, and CSM must be enabled (but you can set everything to UEFI Only within CSM). If you disable CSM then the NVMe device's OPROM will not execute and it will not be bootable. To boot with CSM disabled you must mod your BIOS and insert the NVMe modules extracted from an X99 BIOS, but this has its own share of problems and is beyond the scope of this discussion.