Go with the F-550 if you can afford it pulling a trailer is a BIG PITA especially if your making multiple runs I would buy one but I can't afford the 60 grand. I have been trying to decide what todo for my trucking business I need 4wheel drive and I can't afford a 550 4x4 or a F-450 4x4. I can afford a F-Superduty which is what I have now it carrys 2 yards of gravel but its 2wd I really have tobe carefull of getting stuck.
I thought about getting a F-350 4x4 but the load carrying capacity or the lack of really worries me I'am pretty much limited to 5000lb max for payload. With gravel its pretty rare to keep under the 5000lb mark the F-Superduty can carry upto 8000lbs which I have carried on my previous F-Superduty.
I hauled 6200lbs of crusher dust its the first heaviest load I carried on this truck and it handled it fine I would be concerned about a F-350.
On my trucks I run a 12x8 flatdeck a 8' bed is completely usless for me because I haul lumber also up to 24' long. I have been thinking soon as I add a dump bed to a F-350 it sure would eat up the payload capacity. When you look at the suspension on and frame on a F-350 compared to a F-Superduty there is a significant difference.
Myself I have been flipping back and forth on what to buy trying to find a F-350 4x4 Cab and chassis with a 161wb is like trying to find a needle in a haystack. Finding a F-Superduty with the same wb is considerably easier and I need another truck soon my current truck is showing its age pretty quick.
Like I said I'am really concerned on the F-350 4x4 cutting the mustard I have had 2 F-350s before which were 2wds they were easy to overload.
This is my second F-Superduty the first one was gas but it did have a dump on it worked great except for it got 6 mpg max. My current truck is a diesel it gets 11mpg max it has a straight flatdeck with no dump and I need a dumping flat but I don't want to convert this truck as it needs alot of work.
Its been a real toss up I have been trying to figure out ways of converting a F-Superduty to 4x4 cheaply I really don't want to loose the payload capacity.
Back to your point the F-550 will carry 9000lbs of dirt fairly easy thats more than a dump trailer can handle and you have the manouverability of a single truck.
I don't know what insurance rates are in your area but I don't think your gonna be any cheaper to insure a trailer and a truck.
You will really have to think about where you are going tobe delivering to if your not going tobe able to get a trailer into the places why own one.
In my line of work 90% of the places I deliver to a trailer is not even a option if a trailer will fit a tandem axle dump truck will go. For me my work is the people that want 2 yards or the road is too small to get a large truck down so I make multiple trips.
Get the F-550 you won't be disapointed
Good Luck