The axles and brakes are bigger on the F450, but they also weigh more. On most of the years, the F450s also come with 19.5 G rated tires that are rated higher than the F350s although the tires are also heavier. I know that my 14500 rated truck does really well at 14400.
If you consider the tires only since the axles are obviously rated higher than the F350s, the F450s are more capable. For sure, the turn radius and brakes are awesome on the F450s although you'll feel pain at the pump with 4.30s vs 3.73s with all but the heaviest loads.
On the other hand, at 14400, my truck with 4.30s will accelerate easily over any mountain between Seattle and Yellowstone at any speed that I'd want to travel. I bought my F450 because I felt like heavy loads were in my future and with heavy loads, I'd rather pull the mountains easily than get 1-2 mpg better with a lighter load.
I figure it probably costs me at most a couple of $20s in fuel on most of my longer 400 mile trips.