You should be able to find the "actual" weight on a sheet that is probably pasted on an inside wall of a wardrobe closet. It's true that a light class C on an e-450 rides harsh, I have one, but it does make it a little less prone to sway. The e-350 will have a slightly taller gear ratio than the e-450; therefore, it might get slightly better mileage. The e-450 will have better brakes because it's rated for more load. In earlier years, the e-450 had a rear sway bar that the e-350 didn't have. I don't know if that's still the case.