I've seen this question, which has no accepted answer, it is implied that the cabin size is only a visual change and doesn't affect the gameplay.
But this is about the chassis. I've seen screenshots of trailers that (from the looks of it) just wouldn't fit on a 4x2 truck. So I'm wondering, if you refit a truck from 4x2 to a 6x2 or 6x4 do you only have the downside of the reduced tank capacity? Or do you gain anything, like the ability to tow larger trailers with more valuable goods?