ArchAngel, You're correct on all counts.
Yet, I clean my guns, Dirty means nothing to me, and I don't find it particularly dirty. Accuracy means a lot to me.
Unique is a wonderful powder, that I believe contributes to accuracy, because it causes the bullet to obdurate like black powder.
A lot of the "old" powders are still some of the best choices. Bullseye is an example, but not my recommendation for non-Ruger .45 Colt loads.
Go to a Cowboy shooting match, and you'll find the vast majority of those that shoot .45 Colt are using 255Gr LRNFP and 8.0-8.5 Gr of Unique.