Yee gods , I shot 400 gr Speers out of my No 3 at those speeds and it was very ugly , 500's must have been nasty to say the least . Eventually I settled on 405 hard casts at about 1600 fps , nice to shoot and worked great on game .
To the OP , as others have pointed out , there are better platforms for a 458 WM . That being said , they are a very cool rig . I had one , along with a thumb safety Tropical M 77 in 458 WM , some years ago . I liked both of them very much , but loaded them both down to hot 45/70 levels . I eventually sold them off because I carried my Marlin 1895's in 45/70 most of the time . If you've got the itch brother , scratch it . I did and I don't regret it , it's all fun .
To the OP , as others have pointed out , there are better platforms for a 458 WM . That being said , they are a very cool rig . I had one , along with a thumb safety Tropical M 77 in 458 WM , some years ago . I liked both of them very much , but loaded them both down to hot 45/70 levels . I eventually sold them off because I carried my Marlin 1895's in 45/70 most of the time . If you've got the itch brother , scratch it . I did and I don't regret it , it's all fun .