I think it is in the 70's I would say minimum 100 PSI gauge. General rule of thumb on gauges, operating pressure should be in the middle of the span. That is where gauges are the most accurate, and coincidently calibrated most accurately.
My gauge is tapped on top of the oil filter cap. I read 10PSI at 700 RPM idle, 20psi at operating temp and 1200 RPM and 40-45 PSI at about 2000 RPM. When she's cold, as in winter temps, I've gotten as high as 95 PSI running 2000 RPM's.