Both great calibers, but from what I've learned about Africa hunting, they wouldn't be preferred choices. Seems they prefer lower pressures, to prevent extraction issues in the extreme heat. That's why the .416 Rigby is still so popular. The .416 Rem Mag and .416 Ruger (.416 Roy is a lot more powerful, but very high pressures) are nearly identical in power, but the huge Rigby case does it at much lower pressures, and that's a big deal when you're about to be trampled. The last thing you want is a sticky case. The .458 Win Mag suffered that fate in the beginning, and it still isn't popular on the dark continent.
I've also learned, when it comes to PH/Guides, they have .458 Lotts opened up to accept the .458 3". So again, they get the Lott power, at much lower pressures.
By the way, I'm not knocking anyone's choices, or favorites. Just merely sharing what I've learned, and making conversation.