My LinuxCNC desktop locks up periodically

Not sure if you can restart X and the WM without losing all the launched applications.

Can you try the Intel video to see if the problem goes away?

Hyperthreading is disabled on my CPU, that I do know.

# grep -E "cpu cores|siblings|physical id" /proc/cpuinfo | xargs -n 11 echo |sort |uniq
physical id : 0 siblings : 4 cpu cores : 4

Okay, I've disabled c-states. We'll see if that changes anything.