The 4.0L that is in the Pathfinder is a Dual over head cam engine. meaning that it has 24 valves, also meaning that there is more air and gas comming in and out of that engine as opposed to the standard push rod or SOHC engines. Therefore Nissan and anyone who knows a thing or two about engines and fuel will tell you that 93 octane is best for your engine. It reduces pinging and detonation in older engines, and mixes better with the larger quantity of air that is being pulled in by the DOHC. On top of that 93 octane reduces the amount of carbon build up on your internal components due to the higher temps on the detonation stroke. Your engine will run cleaner and longer by using 93 octane. Some more added benifits to running 93 are that you will have better performace, better gas milage, and less maintenance due to not following your owners manual. You may not think you are hurting your car by using sub-par octane levels, and saving some cash at the pump but in the long run you will pay for it in the form of maintenance bills
so to answer your question I ALWAYS use premium gasoline in all of my vehicles. DOHC or not it's still better for your car.