A few things to work through:
Set HTT multi to x3 - then you do not have to worry unless you start to run some very different dividers.
The LDT & HT voltages I use to bump high when running HT 350+ or if you find that CPUz sometimes reports that another copy is running and you know that there is not.
Also set the Chipset fan temps to max at >30C, these fans are quiet and running them at full speed will help drop temps a bit and help stability.
You will be best to really find out what the Chips are on those modules as they may not be TCCx as there is an part indicator implying CAS1.5
On the back get the Product Code and the PN number - I will get the real chips for you from the 'horses' mouth. Then the right BIOS, Vdimm and Slots can be used.
In the meantime run CAS 2.5-3-3-6, place a divider like 133 as I think your stability issues are currently mem timings and these are rated to DDR500, so at a min (CPU allowing) 2.75GHz should run without Mem being an issue.
Work the CPU to see where it will go, run prime for 6-10mins as a quick initial test and at some milestone places Pi32M / OCCT as an indicator - do not worry about times as you can tune for that later on.
Bump Vcore Only when really necessary.
Keep working upwards