The simulated feathure for my TP type is 10% torque which equates to 165shp.
If you take the torque below 10% you are using the prop as a 5 meter disk air brake. You can nearly double the VS using it depending what the flight idle is. Its not unkown to be FL100 on the beginning of the downwind and make a normal circuit and still hit the stabilised approach gate at 500ft at a sea level airfield. One of the joys of having pressurization and not worrying about engine cooling.
There is quite a good article out there by a BAe test pilot for the twin drivers about when to nurse an engine running ruff and when to shut it down. The jist of it is that if the engine is not meeting the simulated feathured power output you shut it down otherwise you won't have enough rudder authority at low speeds.