So, you are essentially looking at a 23, a 25 and a 27 footer, (as "generally prevailing" custom includes the overall length), two of which are currently in development. Larger trailers come with more space but require correspondingly larger sites. If you are oriented towards the older sites at the national parks, longer trailers will be more limiting, as they can be in high-season Florida and other destinations. A fifth-wheel configuration would mitigate this, but it sounds like your sights are set on a larger cabin. Joining the Airstream forum and RV.net will expose you to the views of more folks who deal with larger, heavier trailers than commonly prevail here.
I suggest basing the tow vehicle's capacity on the trailer's GVWR plus whatever additional margin might make you comfortable. In particular, limitations imposed by the rated payload capacity, particularly on highly-equipped trucks, can make the rated towing capacity unobtainable. I believe you would be best served by understanding and carefully reviewing every rated capacity in the whole alphabet-soup. Regrettably, while you may meet salespeople who are more knowledgeable than you, none will ever have your interests at heart as much as you will. So, it's caveat emptor.
These are three different manufacturers, all respected, all with different approaches. We shot over a hundred pictures during our factory visit, many with a tape measure in the frame. But the basic, and somewhat surprising to us, decision was made there on the factory floor; the pictures generally served as much as mementos as planning tools.
You have some enviable choices lying ahead of you. I would enjoy hearing more about how all this plays out.
~ “It’s absurd to divide people into good and bad. People are either charming or tedious.” Oscar Wilde ~
~ “What the human being is best at doing is interpreting all new information so that their prior conclusions remain intact.” Warren Buffett ~