The .450 Rigby is indeed a beltless .460. Paul Roberts, the previous owner of Rigby, spawned the cartridge specifically with elephant in mind as he felt that the .450's and up did much better on body shots. As you can imagine, breaking a bull elephant's shoulder takes some doing and a 500-grain .458 bullet certainly has a bit of an edge over any of the .400 calibre cartridges in this respect.

Regarding collector's value, well, that would depend on the kind of rifle, wouldn't it? "Original", ie London-made Rigby's, obviously have a lot of collector's value. CZ's, although very fine rifles, would not have much.

What kind of rifle were you interested in buying?