I bought a 458 Express, with the idea of converting it to a 450 Rigby. Well I love the 458 Express (I shoot a 500gr between 2250 - 2300 Fps. I do not need a 450 Rigby shooting 500gr bullets at 2400 fps. Yet, I still want one.
I think it is a great cartridge, and even though it is one of the newer 458's on the market, just because it is a "Rigby" adds a bit mystique to it.
Something I have noted with people who own it, is that a 500gr @ 2400+ fps is to much to handle to for most people and not enjoyably, same applies to the 460 Weatherby that I have seen. They all load it to 2200 - 2300, which is Lott/Express territory (and probably the ideal combination - yeah I know lower pressures for the Rigby).
Basically then you have a very expensive round and rifle probably, doing the same as the others... A bit like most of us driving pickups / Big SUV's in city traffic next to small hatchbacks... Why do people do such stuff, having big cars, big calibers, well just because it is what we/they like. If people want to own a 450 Rigby in say a Rigby and load it to a more "moderate" load of 2300 fps, fine with me, they have the rifle and caliber of choice and at those velocities still excellent. Maybe 2400+ may be to fast...