Little doubt about T compensation: I thought there was an on board thermometer, but the addition of this feature means it's not the case?
That is not necessarily true. the compensation is just something to play with to help you get in the "BallPark" of your choice. It also helps adjust when your room temperature is not exactly 68 degrees F (which mine never is). I would be very surprised if the SXM didn't have an RTD sensor on the circuit board.