As you can see - there's no one answer to your question. It varies depending on things like how much wear and tear is on the engine (as the bearings/clearances open up, pressure drops), weight of oil, temperature of oil, engine rpm, etc. A generally accepted rule of thumb is that you want 10 psi of pressure for each 1000 rpm (6000 rpm would like to see at least 60 psi); and a minimum of 15-20 psi at idle; more would make me feel more comfortable. Most pump have some sort of internal spring-loaded bypass that limits high pressure to some preset level. Stock type pumps are usually set so they won't exceed 60-70 psi.
Mine when cold (0 degrees - 90F) will jump straight up to about 65 psi at idle or with higher revs. As the oil temp increases, that pressure drops off a bit. At 210F oil temp, mine idles (800 rpm) with about 30-35 psi, and with revs hits a max of about 55-60 psi. My short block has about 66K miles on it - original rings/bearings. The oil pump was replaced with a new, stock pump at 52K miles when I pulled the motor for performance upgrades. In winter I run 5W-30 weight oil; in spring/summer/fall - 10W-30 or 10W-40 (depending on what's on sale at WalMart).
My engine is relatively new with about 6,000 miles on it and at a cold start, it's about 60 psi. When warmed up, it'll hover between 50-55 psi while driving (depending on the rpm range) and 45-50 while idling.
I use Castrol GTX 10W-40 motor oil and changed it after the cam break in, at 1,000 miles, and at 3,000 miles.
Mine on start up goes to between 65 an 70psi, warm idle around (800-900rpm) it sits right about 20psi an while driving it's right around 50psi shoots up to 65psi if i get on it. My motor prolly has around 5000 miles on it i'm not exactly sure i bought it used 10w30 oil too