I only can go buy what I have read. Boddington and Wieland, along with some of the early 20th century hunters state .404 jeffery and .450/.400 Jeffrey. Jeffery, from what I have read, had the .404 developed with Cape Buffalo as the quary. Look at the ballistics. In theory, more than .375 H&H and less than the .450 Nitro. Enough without waste.
Sort of goes against my favorite hunting quote below, though.