I just watch it for trends, and have on all my diesels. 10° of fluctuation is minimal.
Yes, IAT will decrease as load increases because the EGR flow decreases. That is until the intercooler can't keep up with the increased ambient temp of sustained high boost while pulling a grade at high boost.
For reference, my 05 would run an IAT within 10° of ambient under most conditions, closer to IAT when cruising. On long hard, hot pulls it would get to +30-35° from ambient at most.
If you watch your IAT during a regen when the EGR is closed you can see what it would be like without any EGR.