Oil press on most 4.0L's is about 60 when cold, but comes down to 40's when in idle and warm.
When hot, press can drop down to 20-40psi in idle. Depending on mileage ect.
Freeway speeds should yield a minimum of 50psi but no more than 75 or so.
Some worn XJ's can idle with as little as 10psi. (250,000 mi)
Rule of thumb: 10 psi per 1000 rpm or 6 cyl.