Hi all, since there was some speculation about the actual temperature maximums for the Z9 mini, I contacted Bitmain and received the following information:

Ambient temperature: 15-35C
PCB Max Temp: 80C
Chip Max Temp: 125C

I was told the PCB and Chip temps are the thermal cutoffs where the unit will shut itself down. Also interesting that their specs on the Z9 mini info page state an operating environment temperature maximum of 40C, but they told me 35C when I contacted.

This is all FWIW, but figured it might be helpful. Also explains why in my environment, when I have the fan set to auto, my Z9 regulates itself to mid 70s C, despite having lower temps possible with a higher fan rpm. Seems 70-80C is perfectly safe for the unit.