Rebore the 458 win mag to a Lott. The Lott is a great caliber, and you can load it down to 458 min mag, with
less pressure.

If you want a lighter rifle, like a 416 Rigby, sell it and buy another CZ in 416, so you don't have to rebore to 404.

Try and get the biggest case you can, and reduce pressure, and recoil.

The 458 Lott is a great caliber, but pressure is high.

Another alternative is to rebarrel and rework the 458 win mag, to 500 A2. The 500/510 Wells kicks near twice the
458 Lott, but, it's supposed to be a considerable step up in power...

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When I buggered the front bead on my .318 this last safari, I used my .404 "heavy" as my backup on plainsgame. I like the .404. It knocked both a blesbuck and an nyala down so fast the former was dead before the dust settled. The nyala would have gone the same way, but I hit it a touch too far back. I'm thinking of experimenting with North Fork 380 gr. semi-spitzers at the traditional British velocities as an African medium and saving my black, all-weather .375 for the Arctic. That way I will have a peep sighted medium for most game and can use the converted Pedersoli .450 #2 for the heavy or I can use the .404 at German velocities for my heavy and take the .318 back again. Either way, tradition and effectiveness are marvelously joined. So rebarrel it to .404 and put a good Williams peep on 'er. You won't regret it.