I'd like to "like" just about all the posts! But instead just a quick thanks to the contributors, this has been a great read.

So the jist of this (from what I gather as a new reloader) is:

-The COAL in the manuals are minimums to keep pressures safe.
-Accuracy MAY be increased by seating a long (keeping gun function in mind), without increasing pressures to unsafe levels.
-If one goes off the books, use a min COAL and start seating deeper if desired with lower charges and work back up, because pressures will rise.