I'm not sure which ones are originally .458", but there are a few nice 500/450 variants to choose from.
The 500/450 No.1 Express is nice choice for both hunting and target shooting.

An issue with some of the Brit chamberings based off of a .450 case is rim thickness (or thin-ness as it were). This could be avoided by chambering up to a .500 based case.
I have noticed by my own measurments that my 500/450 No.1 cases from Kynoch have a .035" rim whereas the Westley Richards brass has a thicker rim very comparable to Bertram brass of the same chambering.
Unfortunately, by doing this, the extractor would have to be altered as well, or a new one made.
Apparently this was already done when the action was rebarreled to 45/70 so it has lost it's originality as far as that goes anyway. Problem is, if you eventually want to go to .461, it would be nice to be sure that the existing extractor could work.

Anyone here know for sure if the base diameter of the .461 is smaller/larger than the 500/450 variants?