It just might have occurred to me earlier with the System running consistantly between 70°C and 110°C:

Macbook Alu fan heavily blocked by dust (front picture)Macbook Alu fan heavily blocked by dust (front picture)

Macbook Alu fan heavily blocked by dust (side picture)Macbook Alu fan heavily blocked by dust (side picture)

 

Previously, the fan ran at maximum speed, the temperature went up to 110°C at full load, though performance dropped, presumably due to Intel™s CPU safety measures.

Now, idling fan runs at lowest speed, temperature is below 50°C, even at full load, the temperature stays below 70°C.

 

Bottom line: if you encounter performance, temperature and fan noise issues, check that the fan outlet is not full of dust. It helps a lot, neraly as if I got a new machine.