Welcome to CHR!

First, my newly built SBF, everything new idled at about 20 to 25psig, then increased to about 40 or 45 with RPM after it was warm, so I wouldn't be too concerned with that part. The first things that come to my mind when oil pressure falls with RPM are 1) oil level low, starving the pickup, 2) oil filter restriction/very dirty or 3) an oil pump problem. You've said that it's a higher capacity pan with the right amount of oil so #! shouldn't be an issue. It's hard to imagine that your oil filter is the problem, but it might be worth the cost to replace it with a quality filter, like a WIX Gold or ?? so I'm assuming that the most likely is a worn/damaged oil pump. You mentioned a piston failture, so there could have been fine metal passing through the screen and going through the pump, so I'd probably be looking at replacing the pump. Considering your professional build I'd go with a standard pump, not a high capacity/high pressure, but that's just me, others may disagree (how about it Glenn Sexton?). It's likely that you'll see better idle pressure, too.
I would for sure change out that plastic line going to the oil pressure gauge. I use a sending unit style, but a direct piped unit takes away any questions - it is what it reads, but that little plastic pipe getting on a hot surface is a disaster/huge mess just waiting to happen.

My $0.02, and again, glad to have you here!