If you are cruising at 380(max 381), 4 kts upper margin sounds correct but to MMO ..
If your speed stayed within the upper margin,how close did it come to an overspeed,if you do it again please take a picture and post..im interested.
In any case flying at max will get you in the overspeed one day or the other.
. Also on that topic, what is it giving you? Nothing relevant in my mind. It is telling you the speed at which the airframe/wings can handle 40 degrees o
You must be flying in easa land,the FAA
use 1.2G(33 deg bank to clacker).