Why would you go to thicker oil in search of a number? Thicker oil equals less flow. The pressure number is greater do to flow restriction. What does this accomplish? Nothing. If there is sufficient film strength between the surfaces to prevent metal to metal contact that is all that is required. If the pressure is not sufficient to prevent metal to metal with thiner oil then there is to much internal leakage. Personally I have no issue with 20psi idle and 55-65 at speed. I've run 60@7100 for 200 passes with a big block. Larger journals, therefore faster surface speed which by all rights should require more pressure than a small journal. Just checked the bearings, perfect. 5w30, 25 psi hot@1200,60@7100. I will say that I first ran this motor with only 40psi@7000 and the bearings were "shiny" after 25 passes. 40psi was not quite enough to prevent contact, just barely. The issue was to much oil though the pushrods. Restricting the oil upstairs cured it. Since you have no feed to the lifters Id be looking at cam bearings, rocker shafts. Assuming the mains and rods are in the ball park.
Doug