these all are tight tolence motors if you built a "old" style motor to the same tolerences you would use 5-20 oil in them too like some race cars
basiclly i would say your just grinding your cams down guess that will save gas (if your valves don't open as far)
i would say if your having a oil pressure problem and its hot try 5w30 or in bad cases 10w-30

i am not suited to a new verihickle if i had oiling problems with an `04 i would wax it up real good and shove it up the dealer's...well you get the point