The .450 will be better with smokeless.
Since you already have dies and I presume they will size cases small enough to hold a .458" bullet(mine did), the only problem might be finding a chambering reamer with a replaceable pilot so you can get a .450" (or .449") pilot for it, to fit the .458" barrel's bore for chambering.
Too, the very much oversized throat on that chambering reamer might cause accuracy problems with .458" bullets.