I think you hit the mark when you said that the 9.3x62 and 9.3x64 are close to the .375. They're too similar, and the .375 is much more readily available and a lot more familiar to people.
.416 Taylor is a neat cartridge, but it's really needlessly overpowered for anything in the lower 48 with the exception of grizzly.
Were I to build up a rifle for myself from one of these actions, I'd probably get off the Continent and pick one of three cartridges...
.425 Westley Richards (If I thought I needed something that powerful), .333 Nitro, or .256 Gibbs.
Bullets and brass are a freak show, though.
And why those three?
Why not?
