I thought about that at one point and purchased a few 40 footers but I haven't unpacked them. But when you think about it, think of the 8 or 8.6 feet for the 102 inch wide trailers, which most are. 11 feet tall payload and youre at 30 feet, including the ratchet which that will also give you a few inches more. You would be getting close to watching out for any bridge under 13.6 at that point.
I haven't been doing this for too long. Only a couple of years now but i have yet to need anything beyond 30. Watch now that i have said it....lol.. But Its really all about preference. Having 40s won't do any harm if thats what you want. I just think its a little over kill for every day normal none over sized loads.