Alright so two CPUs failing in the same system has gotta be strange; mobo issue?

Secondly, what BIOS settings should I be using to run safely? Is XMP/whatever the AMD equivalent is safe? If I don't run XMP then my RAM runs at way below spec (for the stick) default speeds.

Anyone know of a good guide for this stuff?

XMP is technically overclocking, nothing inherently safe about it. I've had new dual channel kits fail memtest at XMP settings on Ryzen, it seemed to depend almost entirely on what the individual CPUs memory controller was capable of.

Maybe the situation is better on DDR5 platforms.