The true bulge can vary depending on rim width, plus you don't want to run them too low and get tire separation going. There is a reason they want you to run tires at a certain pressure. As others have said the higher the pressure the less rolling resistance they'll have but they will wear in the center faster. About the best suggestion I would have is when on the street run them at the vehicle manufacturers specifications not the maximum tire pressure on the sidewall of the tire, that is the maximum that the tire can handle not the mandated pressure. If you notice everyone here for the most part says around 30 on the street and that is pretty close to the vehicle manufacturers spec.
Offroad really depends on what you are doing, mild to moderate wheeling I'd suggest 15 psi., hardcore 10 to 8 psi.
