If buying a new truck, I would sure consider getting the three quarter ton truck with a 4.10 rear axle.
Safety for your family and others is a big issue and the three quarter ton will have larger brakes, suspension, tires, and transmission which all add up to a better, safer tow vehicle.
If you plan on keeping the truck for as long as you say for 11 plus years, the slightly higher cost of a three quarter ton will be very little spread out over 11 years.
Plus, you will enjoy towing a dry 5,500 trailer much better, IMO. Good luck on your decision.