Cold oil will pretty much always hit the bypass limit of the oil pump, at any RPM
On my Dodge when cold the max oil pressure I will see is 68, and this is cold or 3k rpm.
When it is hot, the ma pressure lowers to 62PSI, but it takes much more rpm to reah this maximum.
Thicker oils will raise oil pressure when hot, at lower rpms, compared to a thinner oil.
A quick difference in oil pressure readings for the same general temperature and rpm might be related to a failed oil filter or perhaps the oil itself got diluted with fuel making it thinner, or several other less likely possibilities.
They say as long as you have more than 10PSI per 1K rpm that is enough
it is NOT oil pressure keepinng metal fro metal in the bearings, it is the oil film strength. Oil pressure is more an indication of the rate at which oil is being pumped through the engine, and more is not always better. If it was we should all run 80w-90 gear oil and have the oil pump in bypass the whole time at 60+ PSI.
The seting of the oil bypass can be changed with either high FLow or high PSI pumps. High flow pumps pump more oil per revolution, high PSI pumps might do that and also have a higher bypass rating, the high flow pump could have the stock oil pressure PSI rating, it just gets there at lower rpm.