I followed this with great interest, in particular because at some point, I will probably upgrade to a 5er, although that's a long ways in the future.
I think the one point I find very interesting is, OP asked a question, and as a result, one would expect to get some answers that one doesn't agree with. BUT, when you ask, you have to deal with answers you don't want to hear.
In the end, I don't think anyone is arguing that OP is the one who gets to make the decision, and is the only one who can make the decision. And yes, OP gets to have his own interpretation, which he did. When you share your interpretation, and ask for others to comment on your interpretation, then by default, you get what you got. If OP wasn't interested in other interpretations, then the question should have never been posted.
This happens a lot of forums, and unfortunately it is what it is. I find it equally amusing that some can post something like I've researched the need for EGR monitoring and asked lots of people, and got different answers. So, they come to a forum with thousands of different people, and expect something different?
I have to say the debate of what a trailer weighs seems somewhat comical. The trailer weighs what the trailer weighs, and just because some of the weight is sitting on the rear axles (ie pin weight), doesn't change what the trailer weighs. And, the truck still has to pull/move/exert energy to pull that trailer. The energy exerted to move it doesn't change because some of it is in the bed of the truck. At least that's how it would seem to me.
The curt website defines Gross Trailer Weight (GTW) as
the total weight of a trailer when fully loaded in its actual towing condition; typically used together with tongue weight to help determine whether or not the trailer can safely be towed by a particular vehicle;
I assume tongue weight and pin weight are interchangeable, since I couldn't find anything to say that PIN weight is subtracted from the Gross Trailer Weight.....
EDIT: The definition on the Curt website would seem to align with the belief of most people that the total GTW is the trailer weight, as it sits, fully loaded. And the Tongue/Pin weight, albeit a separate calculation, is not subtracted from the GTW. But, the two variables are used together to determine if a vehicle is capable of pulling whatever it is. Which is what I think Wilber1 and others, are trying to say.
You will never get a consensus on discussions like this. But if you are looking for validation that what you are doing is OK.. you can generally find someone that will agree with you on just about anything.
Mike