I need to do more testing (that is, playing the game), but I think *fingers crossed* that I have found a solution with help from Google's AI Mode! Since my BIOS is a bit rudimentary and doesn't appear to allow me to underclock or undervolt easily, AI Mode suggested I do this instead:
- Control Panel > Hardware and Sound > Power Options > Edit Plan Settings
- Changed Advanced Power Settings
- Expand Processor Power Management
- Set Minimum Processor State to 80%
- Set Maximum Processor State to 95%
According to AI Mode, this works as a "soft" underclock. This *appears* to have fixed it, as I've just played for over an hour without any stuttering, but we'll see ...