Studying powder burn rate charts is interesting for us loading geeks but it's meaningless in a real sense. The experts who produce the data for our loading manuals know, use and list powders that work better for our cartridge and bullet weight and that's all we need to be concerned about. The actual burn rate differences for all powders is pretty small. It's a fact that small differences in such brief burn times makes a significant difference in how those differences preform.
Peak pressure occurs when an accelerating rifle bullet has gone maybe three inches or so. Therefore, we need not be concerned about choosing a different burn rate by barrel length; whatever powder produces the highest speed in a 36" barrel will do so in a barrel half that length.