First I hunt in both Zim. and RSA secondly i use a handload of 54 gr of IMR 3031 /405 gr JSP and a Starline 45-70 case. third I've never even attempted a shot at over 70 yds on any African game. And never saw a PH that would allow his client to do so. I have killed Leopard, lion,buff and most of the plainsgame. For the lighter animals I use a 350 Rem mag and my heavy gun is a single shot W&H 45-70.
I have owned a 416 Rigby but was not overly impressed with it. And the gun now sits in the vault for when i hunt elk. i did shoot a bvull moose with it in BC and took him with 1 shot. but nothing I couldn't have done with a 30 06.
besides ammo is too expensive for the 416 458 etc. when the modern handloaded 45-70 still gets the job done and is steeped in a rich heritage as well.