My memory tells me the lifters need 7 lbs to stay quiet.. If the lifters don't complain I'd forget about it.
As long as you get 20 lbs or more at driving rpm you will be ok.
My first guess would be cam bearings are worn...but that would only be a guess.
The guy that owned my new Jeep put 115K on it with 40W! The only 30W it ever had was from the factory. Seems he had a fleet of trucks and used the truck oil in the Jeep.. You could try a change to 40W to see if that improved the pressure at idle if it bothers you..and it seems it does.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />