I just want to update this thread in case someone with the same problem comes accross it.
I thought I managed to make the CPU stable with the above solutions but all I did was make it last longer before it randomly restarts from a few hours to a day or two.
So in the end I RMA'd it back to AMD (it went all the way to the Netherlands) and got a new one. Been running this new CPU since Christmas and all my problems disappeared. I tried default BIOS settings, previous settings, let it idle for a day with minimal background items running... rock solid stable. I'm also getting much better temperatures and better IF clocks. This is the first time I've ever had a dud CPU and AMD's RMA process was swift and really good. Kudos AMD.
Unrelated: My Beautiful idle temps on an SFX build:
https://imgur.com/a/GmdXq6D