Jim, as far as the seats I can't tell much difference when I use the remote start in winter. After I sit in the seat for a few minutes it does get warmer. I don't think these heaters put enough heat out to make the seats really warm ahead of time, but I'm no expert either.
As the cab heater goes I'm sorry I can't help there. One thing is in my area it doesn't get anywhere near that cold. Thank God