Wolfdog- I can't answer your direct question because I haven't experimented with the newer powders. But do you know about the cast loads that use very small amounts of fast powder? They're loads that were easier to find in older manuals. For instance, Red Dot, Titegroup and Bullseye in amounts under 10 grains can push even large caliber rifle cast cartridges. I'm assuming you want to make plinking loads.
Just a thought. Maybe what you need isn't a new powder, but an old recipe.