What I take away from the age old discussion of bore size vs killing power is: As long as the bullet chosen will penetrate far enough then it will kill.
Now if a heart/lung shot? A small hole will certainly not let blood out and cold air in as quickly as a bigger hole.
A hit to spine? Surely….
An Elephant brain shot? Yes. Bell and others proved that “small bores” will kill just as instantly when the brain is hit. One just has to possess the knowledge of anatomy and the precise skill to absolutely place the bullet.

The issue is; what happens when the brain is missed by a tiny bit or maybe some inches. The smaller bore is going to do nothing much while a larger bore is said to stun for seconds or sometimes many minutes depending upon the size and weight of the bullet. Where is the dividing line? Beats me…..

I would figure that a larger bore against an Elephant is “insurance” against the possibility of a less than perfectly placed brain shot?
.450, .470, .500, .577 from having read the accounts the bigger the bullet, the slightly more room for error. That being said, one has to be able to accurately shoot the chosen rifle otherwise it is all for naught.

Choose the rifle/cartridge that you can accurately use then respect it’s & your limitations

Have I, or will it be likely that I will shoot an Elephant? ….No.
Do I like my .470, 500, & .577? …..Yes. For me they are interesting playthings and lunatic overkill on groundhogs, deer/Elk, or pigs.

-Mike