Good news, I found the issue! Posting in the hopes that it helps anyone else that stumbles upon it.

Looks like the overclock speed I was running on my CPU was fine on Windows 10, but didn't like Windows 11. I've taken it back to stock speed and have no stability issues now.

Cheers for the help @ptx0

Thanks ptx0, I'll update my reply as I run tests. As a side note, it only crashed the PC once (so maybe unrelated?). I recall now on another occasion I had to hard reboot rather than it self-restarting. Aida64 Results: CPU Stress - Ran for 15 mins with no issue and no throttle Disk Test - All tests ...

Game crashes after 15-30 minutes as above. Didn't experience this issue until updating to Windows 11, not sure if that's a red herring. On two separate occasions it has crashed hard enough to restart my PC. I appreciate it's a pretty big base, but I'm not experiencing any UPS/FPS drop before a crash...