Gee, Foax, I hardly know what to say! "Sorry I asked" comes to mind, but in fact, this was among the very few most masterfully comprehensive and instructive series of responses I've ever read, and a credit to the generations of science and engineering professors (and handloading and safety instructors) who raised y'all! Please accept my most profound thanks: I'll be printing out this query and its responses, and posting it prominently in our library of handloading references.
BTW, I was only curious. My own inclinations are to fast powders, relatively full cases, and additive-free bores, but I'm always happy to learn more.
Thanks again for your guidance!