Unless you need (or want) the 4x4, it will have little positive effect on towing, 4x4 slightly decreases MPG (which will be in the 10-12 mpg range anyway), and adds more drive train upkeep.

I think I would give some thought to how much towing you will actually be doing with the truck as well. 3/4 tons are more expensive for up keep then a similarly equipped 1/2 ton (tires, brakes and suspension parts all cost more for a 3/4 ton then for a 1/2 ton). An extra spring (or 2) in the rear spring packs will make a standard issue long box or extended cab short box 1/2 ton truck into a great tow rig if the trailer has he proper brakes and if your really going to be towing once a month or less. Gene