Cast data, experience, and anecdote is split showing that the best cast rifle loads use powders thought of as too fast or slow for the cartridge at hand with jacketed. There seems to be no clear winner between too slow or too fast, although the Lyman and RCBS manuals lean toward too fast.
I've mostly settled on too fast for substantially reduced loads and too slow for those that are just a bit reduced to keep cast happier.
Where do you lean too fast or too slow?