This might be due to a overheat issue.

I just got another GPU lockup while playing the game (after a few hours) and it
did not cause the kernel OOPS/Bug in question, so everything went on as normal
after the GPU recovered.

However, after a few minutes I lost the display (it went black). Logging in
over SSH and checking the temperature sensor revealed that the radeon GPU
reported 127.5C. 

So unless someone else has seen this issue, I think it can be discarded.