I'm going to be a bit of a dissenting voice here.
In my experience, a well built engine with a stock oil pump will hold a (relatively) steady pressure (usually about 40LBS) at both idle and service RPM's; hot as well as cold. This comes from the proper tolerances throughout the engine being tight enough to hold leakdown to a minimum. A stock pump will hold a steady pressure at idle when warm, with the bypass valve dumping the excess pressure at colder temps and higher RPM's.
Large fluctuations in pressure during cold operation and RPM changes usually points to some pressure leakage somewhere in the system, and 70LBS, as indicated above indicates a high pressure bypass spring has been installed. These can be bad on the cam and distributor gears due to the excessive force necessary to maintain that high of a pressure.
I am a big fan of good pressures at idle, since many of these engines are subjected to very low engine speeds during wheeling. A pressure below 30LBS at idle can become 5 or 6 LBS (or less) during a low speed lugging session in the rocks or other technical areas where the RPM's may be forced to drop well below norms (one of the reasons I run a high volume pump).