CZ 416 Rigby is also an option.

What about 375H&H or 404 Jeffrey ?

What about Winchester 458 Win Mag ?
(apart from the fact older ones are Push feed and I would
stay with Mauser 98 style extractor.

Just out of interest, why detachable mag ?
Personally, I don't like them as they can get lost.

458 lott - Reloading option only

416 rem mag which holds more rounds in the magazine for back up shots
Any 4 Shot DGR holds enough - I would concentrate of shooting straight
than having more rounds available.

500 Nitro