I don't need a truck with 20,000+ lb GVWR. The slide-on utility body, compressor, welder and all related tools to my welding weigh about 3500 lbs. Even if I pack another 500 lbs of welding stuff into the new truck, I'm not going to be even approaching the 15,000 lb GVWR of the F450.
I have a 20 foot deck flatbed trailer that I use for hauling metal and other cargo that is too big or heavy to go on the truck. All the extra cargo I usually haul on the truck is just a few lengths of steel up on the lumber rack or shorter lengths in the bed.
The 450 will weigh more than my truck cause of the diesel engine, heavier rear axle and extra tires/wheels and the flatbed and side boxes, but it also won't have the weight of the crew cab body so maybe the truck will weigh 2000 lbs more than mine does without the welding stuff. My truck is 6500 lbs without the welding stuff. So if the 450 weighs 8500 lbs and I add 4000 lbs of welding stuff to it, it's still only 12,500 lbs.
I don't see where I need an F650/750 or bigger truck to haul the weight I'm hauling. A later model F350 dually could haul what I'm hauling, though it would be near it's max capacity. I like to have some cushion, so the F450 makes sense to me.
If my truck was a dually with a diesel and a 5 speed, I probly wouldn't be looking for another truck to haul the welding business. I would just make do with what I have and replace the pickup bed with a flatbed with side boxes to get more storage space.
I have thought about converting my truck to a diesel dually, but realisticaly it doesn't make sense. It would cost $15,000 and for that money I could have a later model F450/550 that would do the job better.
I have to consider fuel mileage and cost of tires and maintenance. The pickup truck sized diesels get pretty good mileage in pickup sized trucks. Some people with the Ford, Dodge and GM trucks with the 7.3L, 5.9L and Duramax diesels say they get 15 to 20 mpg and sometimes more on the open freeway. I'm getting 5 to 10 mpg and it's killing me. I can envision one of those big F650's or bigger only getting similar mileage as what I have now and with more expensive diesel fuel to buy.
We also have to pay the registration here in CA based on the weight of the truck. My fee is assessed based on the original curb weight of the truck, which was 6000 lbs, according to the factory. I already pay over $250 per year to register my F350 and it's an old truck too ('92). The state is talking about doubling our vehicle registration fees to balance the state budget now too! If I have to pay double the fee to register a truck with an unloaded factory curb weight of 10K to 15K lbs or more, I won't be able to afford to keep a license plate on the thing.
The insurance is another thing. I insure the F350 as a personal use vehicle and it doesn't cost too much. The insurance company has seen the truck with all the tools and equipment on it and hasn't said anything about it or tried to raise the rate. There's no way I'm going to be able to convince the insurance company that I'm using a 20K+ lb GVWR truck for personal use, so I'm sure my insurance cost will go up if I get a huge truck like that.
The other thing is parking. I live in one of these stupid pansy neighborhoods where nobody likes to see big commercial trucks and calls out the cops if they see one parked for too long. I get enough grief over my F350 as it is. If I brought home an F650, I'd have to find somewhere else to park it. If I lived out on the farm somewhere in cowville, I wouldn't worry about it, but I'm not so lucky. Believe me, I would love to live in a place where cows are my only neighbors, my life would be alot more fun.
I can deal with whatever is the highest capacity pickup-looking vehicle, which is the F450/550 or Dodge 4500/5500, or the old GM 3500HD but anything bigger is just not practical for me.
If the biggest things I have to worry about with the F450 is a parking brake and a flywheel, I think I can handle that. My truck has been pretty good except for the emmissions/fuel sytem problem lately and I think that mystery will be solved soon. That F450 is very similar to the truck I have now, just beefed up more, so I feel I can handle whatever happens with it.