Please correct me if I am wrong. 1. For electric heat, the branch circuit size needs to be based on 125% of the full load amps. 2. Conductors (under 100A) need to be selected at 60degC unless the terminations are rated for 75degC.
Sounds right to me but I would look closely at the terminations. Most, over 30a are 75c from what I have seen. Of course YMMV so you have to look. Of course if you are using Romex you are stuck with 60c anyway.