You might want to pay attention to load ratings....A "D" rated tire will be a little heavier, will be a little stiffer and should give you more mileage...
Far as actual payload rating vs tire, the factory "C" rated tires are more then enough...so it's makes me laugh when I hear guys going to an "E" rated tire for the Raptor..
Only 2 reasons to go to a "D" rated tire really, one everything being equal they will give a more firm controlled feel when towing, and if you want to get more miles out of your tires then the stockers will do...
But if you tow a lot, did you really buy the best truck for that?...
I've been replacing my tires with OE size and rating and yes they do wear out quicker then higher rated tires, but I really like how the truck performs in the dirt with them and it does go in the dirt...