Brybenn;
The 375 is a do-all cartridge where the 458 is much shorter range and more specialized in my opinion. I have both and many more in this catagory and for your needs I would highly recommend either the .375 or .416. They will do anything in NA and most anything in Africa. I personally don't like the 458 WM and find it very limited in it's capabilities but the .375s and .416s are quite universal in their realm. Forget all the paper ballistics and take it from someone who's been there and done that, the .375 H+H is a hard cartridge to beat, up to and including elephant. Certaintly buffalo are no contest to the H+H in the hands of a man who can shoot it. And it is so much easier to become proficient with than the .458 variants. I have fired thousands of rounds of .375 H+H, .416 Taylor, Rigby and Rem, and .458 WM, Lott and Ackley. Of all of these cartridges I would recommend the .416 Taylor or Rem above all else for ease of shooting, external ballistics, and all around kill anything cartridges. The .375s are next by a small margin as all around calibers and the .458s and .470s are last.