I previously wrote that I wasn’t using the “Dynamic Switching” scheme for setting processor speeds dependent on the processor load because I thought it made the computer running hotter. Again, by accident, I switched to “Dynamic Switching” mode, and presto, the temperature dropped to 42C, and it’s been there since!
UPDATE: And after a few hours the computer just turned black, and had to be rebooted. I’m still running in Dynamic Switching mode, but I need to do some more testing with different voltages. I’ve now just turned all multipliers from 8 to twelve.