The more overbore the cartridge, aka smaller bore to larger case, the slower the powder it will like. The closer to being a straightwall case, the faster it wants. The heavier the bullet for a given caliber, the slower the powder, usually, from my limited experience. My 300RUM prefers the slowest of powders, and its heavily overbore. The 7mm rem mag is also fairly overbore, pretty big step down at the shoulder, and likes powder almost as slow. The 375H&H likes powders in the same range as an '06, and if you look, their cases are similarly proportioned, albeit bigger with the 375.