On the PT6A-27 (Twin Otter) torque is our reference to set power at any stage. In day to day operations, it is uncommon to hit the temp limit before the torque limit, even at our hub (south american airport at 5000ft AMSL, usually between ISA+15 and ISA+20). Since torque is our main reference value, it is adjusted by temperature.
Regarding destroying the engine if there is an over-torque condition, the emergency section of our AFM states that we can redline the engine to the first limit we hit (Torque, temp or compressor rotational speed) if an emergency condition is present. That difference is in the order of 10PSI (80% of the power available) if taking off from a high elevation airport at high temperature. The engine is flat-rated from 715EHP to 625SHP, which surely must play a big part in this discussion (but since my knowledge doesn't go that deep, that's as far as I can get
)