Welcome, lots of Knowledge here.
Don't assume anything. Basically you don't know what weight oil it was. Maybe it was 50 wt.
HOW much did the oil pressure drop? 1psi, or 20 psi?
Did you change the filter too?
Is the new (if) higher or lower micron rating? (more or less restrictive)
What was the oil press., and what is it now?
Was it running at same temperature both times? As in cold, or after it was hot?
Multiple things affect oil pressure.
1. Temperature.
2. How many hours are on the unit. The hour meter is not the only indication.
Accuracy of the gauge/ sending unit.
There is no "Ideal". Every motor is little different It's either good or somewhere between good and bad.
Did you down load and read the TM's? It's in there. "3) Oil pressure gage located on engine should indicate 20 psi minimum"