Hello DanielDuecker,
we could improve the yaw drift from a angular deviation of more than 40° to around 1° with both measures used. (Warm calibration + slow rotation at the compass calibration steps)
But we still need to test this further the see how reliable this is and after which temperature change (air temperature) the problems start to occur again.
Also a part that i find anoying is that you have to wait around 10 min for the IMU to heat up. it really stretches operation times by at least 50%