Using a 3.9 (as in the coupe or sedan) will let you go faster (higher kph) for a given engine RPM. It will extend the speed range for each gear.

On the other hand, there will be less rear wheel torque.

So you'll have less power, but your engine will last longer not being revved up so high all the time. You'll also have a more driveable comfortable ute I would guess.