Thanks Simon for the quick reply.

Not sure where the similarities end between the P8ZZ7-V and the P8Z77-M PRO.

The board manual even lists 4x 8GB 1866 C9 support: 

CORSAIR CMT32GX3M4X1866C9(XMP) 32GB (4x 8GB) DS - - 9-10-9-27

Via at https://dlcdnets.asus.com/pub/ASUS/mb/LGA1155/P8Z77-V/E7074_P8Z77-V.pdf

With CONFIG_NATIVE_RAMINIT_IGNORE_XMP_MAX_DIMMS=n the DIMM's should be trained at 1333MHz but that didn't work either.

In my case even the vendor bios wasn't capable of booting with the RAM, so I guess that is a red flag already.