Go with the 450 if you're going to do the big tires/wheels.
I had a '12 350 and did the 2.5" spacer up front and a block 1' taller in the rear.
That truck towed great.
However I was not impressed with the brakes when they were really needed.. They were good at first, but pushing the pedal to the floor didn't help....
The truck pulled 18,000lbs fine, but I wound up leaving the stock wheels/tires on it because I didn't want to give up the performance.....

I'd say to do the 450..... and I believe the 450 has bigger brakes in addition to the bigger front axle.
The lower gear will let it pull the bigger tires...
If I remember the 450 was around $7k more than the 350.... I thought that was steep...

i just got a 13 f350 with the 3.73, towed about 14k round trip about 500 miles last weekend,got right at 12 mpg, never had a concern about having more gear, pulled the boat out at the ramp at a 1000rpm's lots of low end torque, getting 19.2 mpg riding to and from town

you can get 19.5's on the f450 and 18's on the f350...let me know if you need a quote on some new ford trucks...i'm in Ga Sc area so it won't be a bad trip...Chip

I also have a pre-owned 2011 F450 crew cab king ranch in stock if that might interest you...LMK ..Chip

getchasum I am needing 2 cab and chassis lariat 450's. Both loaded one extended cab the other crew cab. Both 60" CA

Can anyone tell me the difference in the 450 and 550's?

ok...i will get some info tomorrow...you can call me at 912-346-8025..

i will also get that info in the morning...call me so I know exactly what you are looking for
912 346 8025

I pull with an 08 F450 & 4.88 gears... Love it!!

Same here. Fuel economy suxxxs but I drive it about 3,500 miles a year so not too bad.