After setting dev.acpi_ibm.0.fan_level=7 the fan seems to run more consistently/evenly without the constant changes in noise levels which was the most annoying aspect of it's performance, so I think I can live that.
Many thanks for the suggestion.
Above you said (can't get it to quote properly, zenforo is frustrating sometimes!):
> root@EMTEC:~ # sysctl -a | grep temperature
hw.acpi.thermal.tz1.temperature: 44.1C
hw.acpi.thermal.tz0.temperature: 58.1C
dev.cpu.1.temperature: 53.0C
dev.cpu.0.temperature: 55.0C
I hope that's busy doing something? If it's idle it's running about 10°C above where it should be already, especially tz0, almost certainly CPU & GPU, more usually cooler than CPUs.
I assume you'll have its Hardware Maintenance Manual? If not, get it from manualslib (ono) ASAP.
Investigate fan replacement, or at the very least replacing the old thermal paste, but better a new fan, Ebay etc.
I guess you've used canned compressed air to remove dust and fluff already?
Running an already noisy fan at 7 for long will accelerate its wearing out, whereas with a new fan and paste you can expect years more service, and a quieter life ...