@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?