To me, it is more about the locations I am looking to be able to get into. Most RV parks are not the issue, although some will have length limitations and/or limited on spaces that will accommodate the longer trailers. I want to be able to get into areas in the CO high country, no RV park, and tighter switch-back roads are a no-go even with my TT at 30', point to bumper. There are also some passes that I would take my 30' TT over but would not consider a 35'/40'. Again, all depends on your 'wants'.
Remember to keep in mind that a trailer/truck combo of a 40' 5th is shorter than a 40' TT when towing... using the same truck.