I didn't think too much about the .450 as a levergun cartridge, but it made a helluva bolt-action thumper-gun load. It's a fairly easy conversion on a short-mag action.
I've had a .444, and with the right bullets, it was a giant-killer. It had to overcome the pistol bullet stigma when it was introduced, but when properly constructed bullets were developed for it, it became a very useful big-game cartridge.
I have no experience with the .308 and .338, but I saw them as a continuation of the .307/.356 story. They could certainly be useful, but lack of popularity eventually does them in.