There are no flies on the 458wm. AA 2230 allows loading the 458wm to 2150fps plus with 500gr bullets out a 24" barrel. 2150fps with a 500grain bullet makes the 458wm performance slightly better than the grandfather of all African smokeless Dangerous game cartridgess, the 450NE 3 1/4". My personal DG loads are 500gr Woodleigh solids at 2135fps, 450gr North Fork Flat Nose solids at 2220fps, and 500gr Woodleigh softs at 2135fps, all using AA 2230. H 4895 is good too, but not as good as AA 2230. I have tested both powders for heat sensitivity and there is no discernlable velocity increase from about 40 degrees F to 95 degrees F. Even when leaving ammo in the sun to cook. My solid loads have provided excellent performance on elephants, cape buffalo and plains game targets of opportunity. The softs have been great on the few animals I have used them on, including zebra.
If you do not hand load and you are elephant hunting, I would suggest having ammo custom loaded for you. Hornaday 458wm ammo is just fine for cape buffalo. I would expect that any appropriate bullet loaded in factory ammo would be fine for cape buffalo.
The two rifles I take on a dangerous game safari including elephant or cape buffalo are a 458wm and a 375H&H.
Both are legal for elephants and cape buffalo, and the 375H&H is versatile enough for everything. Since DG gets top billing, best to have a spare. (And I'm a lefty, so borrowing a rifle in case my DG rifle goes tits up or missing is going to be problematic.) FWIW, the largest game I have killed with my 375H&H is a half ton plus eland, the smallest a 10lb Sharpe's Grybok. Versatile rifle!
Most DG areas have some cover, but not all. Where I have hunted DG there has always been cover, and most plains game shots are under 100yds. A 458wm shoots plenty flat enough for that, and for most opportunities, if that is what is in your hands. All of my DG hunting has been in Zimbabwe, in the Zambezi Valley, on the Escapment, in the Low veld, a couple of other areas.
FWIW, the 9.3x62 is legal for all DG in Zimbabwe, and has proven adequate for elephant. I think of it as something of a 375H&H lite. .366", standard bullet weight of 286grs, standard velocity of about 2260fps, iirc. Lighter weight rifle on average. Lighter recoil. Standard length action. Standard magazine size (not drop box) gives four or five depending on the action. Easy feeding. I bought a 9.3x62 for my son for his first DG safari, hopefully In a couple of years. He is 15 and can handle the recoil.
JPK