I've got a '99 F450 4X4 with a V10. It weighs just under 10000 lbs empty with an 8' steel electric over hydraulic dump with drop down sides and has a max chassis GVW of 15500.
Unfortunately, with a load of road gravel in the 8 foot dump bed it scales at ~18500 if I'm not careful.
Mi commercial plates allow for 24000lb before the price break, so I think something like an F650 would be a better deal for any real hauling. Anything above an F350 requires commercial plates and insurance (at least through State Farm) in Michigan.
The F450 4X4 does make a relatively maneuverable plow rig with a 9' Boss plow, but a pickup with narrow tires would be a lot better for plowing. A F650 would be too large for my plowing situation.
The F450 is sort of a "one size fits all" compromise, but isn't optimum for any one given task. An F350 would be useless as far as cargo weight capacity goes, as the empty weight with a steel dump is too close to the loaded GVW specification.
Mine is a V10. Mileage sucks (10 mpg empty, 6-7 mpg loaded, and 1 1/2 mpg plowing). I only paid $4800, including the plow, a year and a half ago with 70000 mi. The V10 works out cheaper than a diesel for my use, even with the poor mpg and realizing that gas will eventually return to $5.00/gal, considering I'll probably put fewer than 3000 miles / year on the truck.