My 454 magnum would run at 60 psi at rpm and idle at about 30-40 psi. BUT, I think that the type of guage has alot to do with the readings. My guages are stock from Checkmate, they have electric sending units which are not the most accurate.
Are you running Gaffrig gauges? The merc senders are not compatiable with them. When I replaced the Merc sender with a Gaffrig the oil pressure went from 42 to 60. I don't understand why the manufactures don't spend a little more time and money and make it right in the first place.