You are buying a heavy duty truck and expecting it to ride like a car. Look the 450 may haul the world but is that what you need? The 350 DRW will do fine for you but don't expect any ride quality because the DRW is designed to haul heavy loads also. I have a 250 and i never had a problem backing into a tight space. Turning radius isn't a problem. The ride got better when i added air bags to the truck so you may want to get them for your next truck. Even a DRW benefits from them. I have a 5th wheel and have towed it 30,000 miles in the last 2 years so ya i have been everywhere. We take 3 month trips to see the country. Even with the 3.31 ratio I have in my truck I have never had a problem with the power my truck has.
I would stick with the newest truck you can afford because you are going to haul your stuff down the highway. Make sure it's not modified because you may be buying a can of worms.