If you're running at 70 psi most of the time, then you're likely going over the pump relief which you really don't want to do. Heats and degrades the oil prematurely.
Melling stock pumps (which most are) come with a 60 psi and performance with a 70.
It may be wise to lower the oil viscosity so that you stay below 70 above idle.
Traditionally these engines would idle around 15 or 20 and run at rpm around 45.
If the op has lower pressures and worried, then go to a higher viscosity oil.
010752,
Don't mean to hi-jack this thread.
I thought a little more about what you wrote above and what my engine is doing. I also looked up the pump part number on my bill from the engine builder and went to the Melling site based on D_B's post. The pump is a Melling M77HV high volume pump. The pump pressures vs. rpm that I stated are correct, but what I didn't think about and should have added was that at cold start-up idle (say 1200rpm), the pressure is the highest it gets and is about 75psig or so, but distinctly different than the normal hot cruise/rev pressure of 70. So this may be the maximum the engine can develop considering operating temperature, viscosity, clearances, rpm and pumped volume (not considering the bypass spring setpoint), or it may be the pressure at which the bypass opens or it may be the mechanical limit on the stock in-car gauge. I don't know which, but the fact that I get a higher reading when cold, tells me that the bypass is not opening when the oil is hot.
On a quick run-through, one would think the the oil pressure would keep building as the rpm increases. It obviously does increase to some point, but then it peaks there. It seems that the thing that keeps the pressure from continuing to rise with rpm (at pressures below the bypass setpoint) is the fact that as rpm increases, more oil is lost from the rod bearings as the centrifugal forces increase. I'm getting this from reading on the Melling site. So thinking about the rod bearing throw-off as kind of a pressure regulator, what you wrote about increasing the oil viscosity to raise the pressure at rpm makes sense since less higher visocity oil will be thrown off. Of course, it's part of the general concept of increased pressure due to flow resistence at a given volume (pumping water vs. molasses). That has the same effect as tightening up the clearances. Sorry if I'm rambling, but I never really thought or read too much about this before. I just jacked myself up one notch from dumbass.
So yeah, the OP should up the viscosity, until it's rebuild time.