I've had both SRW's & DRW's. I've been hauling with a DRW since 1998 (our 1999 F350) and I will never haul with anything else.
Consider what happens when you are pulling a heavy trailer and one of your rear tires gets punctured...would you rather have 3 tires holding up the trailer at that point or 1? Also, you will love the dually when hauling in a crosswind... you can see the trailer swaying a bit, but you don't feel it.
Two negative aspects are less traction in snow with four tires in the rear and you have to pay 50% more for a set of new tires.
Our current tow vehicle sitting beside our trailer here in Yellowstone National Park is a 2009 GMC 4x4 3500 DRW extended cab with the Duramax diesel. I love everything about it except the ground clearance and the manufacturer. It hauls our 5th wheel much better than the '99 F350 7.3L so you might consider some Banks accessories for your 7.3L when you get it.
