I believe the rule applies to the state in which you are driving. Doesn't make sense that California would limit its residents from driving a 42 foot rig, but let everyone else do it...
With that, whether you get stopped for being over length is an unknown. I suspect with the 40'2" rig, you would probably not have any issues. But, the longer you get, the more likely it will be noticeable that you're over-sized and draw attention.
Also, you're going to want a tow vehicle big enough to hold 4 adults and 1 child AND be able to tow that big of a TT/5er.
