I think this could be a hardware issue?

This is x6 Multiplier in memtest x86


This is a x10 Multiplier in memtest x86


Notice how the SAME BIOS settings, just with a different CPU Ratio the memory bandwidth drops from 5445MB/s down to 5267MB/s
I reported this issue to ASUS in July, but as of yet I have not heard anything back from them
John