Ford's payload capacity confusion

I would get the max tow package. That package gives you a wider front axle and the 4.30 rear end.You will love the improved turning radius of the wider front axle. My F450 crew cab, long bed out turns my wife's Ram 1500. Unloaded, you will get fewer mpg than with the 3.73; loaded, the difference is almost negligible. You will definitely appreciate the the 4.30 in the hills and mountains.

Any dually will serve you well. The advantage of the 450 is better brakes and a heavier frame.