Possible explanations of 10 psi loss of oil pressure at cruise

Thank you so much for the explanation. I was trying to wrap my head around his issue and understand the culprit, but I was stuck on that sender versus what I know of, well, Murphy Switches. That micro tube or capillary set up is my experience, a lengthy one on a wide variety of engines.

Viscosity is fine, and also 50 psi at 1000 rpm is plenty.
For your future reference, at idle even a bit less than 30 psi would still be fine.
You do have a surprisingly high pressure at 2k rpm, but better than the opposite, anyway!

Consider swapping gauges between engines, see if the issue follows the gauge? Repeat with senders?

In reality, 70 psi at cruise is a NON issue or really anything over 40 psi at 2000 rpms.......I just delivered a yacht with the same engines and at cruise it only made 50-60psi.....

I have similar pressures on my MAN’s with about 45 psi at cruise and running 15W40. I wouldn’t worry too much about the pressure you are running at as it sounds pretty normal.