Well, I amicably but totally and strongly disagree
Professor Mawla...
Not to repeat endlessly previous posts (see my post #55 on page 3) but based on experience from many pros, there are two REAL differences. The .375/.416 will certainly kill them, we all agree, BUT:
1) a close miss to the brain with a .45+ will likely give you (not "guaranty" mind you, but "likely give you") one stunned second or two to place a killing body shot. A .375/.416 close miss to the brain will almost certainly not.
2) a .45+ will give you considerably more reliable stopping power than either .375 or .416.
You can decide for yourself whether you could use an extra stunned second for a backup shot, or if you are happy with your PH killing your elephant for you; and whether you need no "stopper" rifle because your PH is supposed to do that job for you.
Call me selfish, but I personally prefer to kill my own elephant; and call me pessimistic, but I personally prefer to NOT gamble whether the PH will actually own a big bore (this is far from being certain!) and will shoot reliably that day (if they all did, no accident would ever happen).......
Live up to your screen name and get a .458 Lott barrel for that R8
If truly .375 is the only option, certainly a 350 gr slug gives you a bigger hammer, and this seems to be important for brain shots.
If you have eliminated the brain shot as an alternative for yourself, then yes, a .300 AFrame or TSX will do the job on a double lungs shot.