I would take the 4x4 option. It does come in handy when trying to maneuver in swampy grass/mud after a rainstorm. Also if you intend to do some boondocking.
But mostly I'd get the 4x4 because of the boat. I've lost count of the number of pickups I watched burn their way up wet, slippery, mossy launch ramps - always with the buddies standing on the bumper. Very entertaining ! I would then just put mine in 4x4 and motor up the ramp. I watched my buddy's dually have trouble pulling his 30 footer out of the water one time in Florida - he was sliding back and forth sideways before he finally got traction. There's just not enough weight over the rear wheels on pickups - especially on steeper ramps.
Also get the limited slip or locking differential. It's usually a cheap option and comes in handy for those sudden situations where you really don't have time to get into 4x4.
I have a 2013 4x4 F350 dually and it tows my fiver just fine.