Joined just to give a huge thanks for this effort. NVMe booting was my goal to free up a SATA port on a backup server. Microcode updates are an unexpected plus. XMP/1600MHz continues to work fine.
TIP: flashback wouldn't work (LED blinked and then was steady on) until I unplugged my DVI monitor and PS2 keyboard (not sure which or both were the cause).

@hancor first of all, thank you for your effort!

I flashed my Z87-PRO (Rev 1.02) and verified with HWINFO that is with the correct version. I also checked the Meltdown and Spectre patches with InSpectre as you suggested.
All seams right, except that my drive doesn't show up in BIOS when I disable CSM. With CSM enabled, It shows as "PATA SS:"

My SSD is a Western Digital Black SN750 SE 1TB 3D NAND NVMe.

What am I doing wrong?