Oils with more viscosity or pumps with higher volume are not going to fix the problem of excessive clearances in the engine. If you have too much clearance on your mains, rods & cam maintaining pressure is a losing battle. Dave told you initially that a high volume oil pump and a stock pan is a recipe for disaster. You can suck the pan dry before oil can have time to drain back down from the upper end, starving your pump. Did you put in an extra capacity pan, baffled to keep the pickup primed, along with the high volume oil pump?

Are you running a PCV, and if so do you have a breather in the opposite valve cover to relieve the suction pressure of the PCV? Strange as it sounds, that alone can affect your oil pressure.

And just to be clear, what the guys are saying is that PlastiGage is not a reliable measurement method for bearings. If your journal or bearing has any deviation from being perfectly round the PlastiGage will give you a bad reading for the spot where you place it. You need to use inside/outside micrometers, measuring multiple positions on each journal/bearing to know your actual clearance.

Keep the dialog going, and I'll bet that you'll get to the bottom of your problem pretty quickly.