I wanna just call horsecrap!

To me, this is a simple case of your obvious conformational bias showing. You know your design choices are right, and all data is interpreted to support that conclusion.

But I am often wrong. So I'll actually ask a question.
How does adding safety and capacity ( building a slightly longer boat) for very minor dollar cost relate to climbing the design spiral in yoyr mind?

And how is building a 30' 4tonne cat a better, safer, cheaper choice?

Your feedback is informative to me though, in that it suggests even you don't know why 30' is such a magical number, to you.

I think it would have been nicer to just say you don't know. But perhaps you don't know that you don't know.

It's hardly sporting to call out climbing the design spiral, without actually pointing out what you see as a better set of choices. Or at least point out the objectionable choices.