It may just be a BIOS issue and might be fixed with a future update, but for now the memory modules I have bought do not work with the M8R and the 1302 or earlier BIOS. Not the full set of 4 anyway! I can run any combination of two modules, no problem. But not 4.
Tested with Memtest86+. Motherboard: Maximus VIII Ranger; BIOS 1202; memory Kingston HyperX Fury Black 2666MHz, 4x4GB set
Results:
1. 2 Modules, 2 full passes, 0 errors
2. 2 other Modules, 2 full passes, 0 errors
3. these 4 modules combined, 5 minutes (less than 20% of pass 1), 434 errors - cancelled the test at this point
4. 2 Modules from another set, 1.5 passes and running, 0 errors so far.
Kingston states it's modules should work with all Z170 boards, ASUS listed a few of Kingstons modules on their compatibility list, among them the 2400, 2800, and 3000 MHz versions of the 4x4 set, but that list is from august.