Hey, I’m coming from an issue I posted: Freezing During GPU Load. I find that this issue is very similar to mine, but my laptop freezes instead. After you talked about the issue, possibly being about the path of the GPU reading from memory. I had the idea to swap the slot my memory was in.
I have a 1x16GB 4800 from Crucial, and it is normally in slot 0 (Left). When it is in that slot, I get freezing under load. However, when I switched the stick to slot 1 (right). The freezing turned into instant rebooting.
Maybe try switching the slot your RAM is in?