I used the 416 REm and the 404 Jefferys for years and could not tell any difference in the two on buffalo hippo, and I used the 450-400 double and it suited me...I used the .470 and 500 N>E. and decided they were just too damn heavy on those long trecks and slow to get back on targets ..
My favorite bullets were the North Fork cup points and Woodlieghs 450 gr. 40 caliber bullets..
Never felt a need for the bigger bores after a few kills, results were the same...A stopper is a plug that keeps water in a tub, good shooting with proper bullets to the brain or spine is what kills large animals pumped full of adreline in their tracks..