You're on the right page. Your engine is really worn out so the bearing tolerances are greater and the oil is flowing through very easily now, thus less pressure. The thicker oil is obviously harder to push because of it's weight and like you said, it's harder to push through the bearings so it's causing higher pressure readings.

What matters here though is volume, your pump can't change the volume of oil it pushes, it physically can't, like a water pump for a given RPM it will push a certain amount of oil. I honestly don't think it matters one way or the other what oil you run. You might be a little better off running a thicker oil but it's hard to say one way or another if you'll see a difference in bearing life because of it.

 

to each his own...