Hrm, thanks. The linked model is a Latitude, rather than an Inspiron, but it’s probably the same sort of thing - I’ll give some of that a try.
Most of the time immediately before the overheats the fan is doing somewhere around 5000 RPM, so it’s definitely heading up there - which is far more than the equivalent on Windows from what I saw doing the same benchmark there. I ran a BIOS update yesterday to no avail, sadly. I’ll try setting the fan to 100% manually and then running the benchmark, though.