Generally speaking torque is the gearbox limit and temp is the engine internals. In some cases (like the -34 installation on the Twin Otter), the original -27 torque limit of 50psi is still the limit for airframe and Vmc reasons. If you exceed the design airframe, Vmc, torque limit, actual Vmc WILL increase.
Sick engines will reach temp first before reaching the torque limit...but that's another discussion.