Hatari,

I don't think there is a "best" calibre.

All mentioned by you + many others will do the job.

I also totally agree with Shakari - even if you hit an
elephant in the foot with a 700 Nitro, it ain't going to do anything
but piss it off and have it piss off out of the area.

I personally think hunters should concentrate on hitting the animals
in the right spot.

In addition, not that many can handle the recoil of the calibres you
mentioned - especially if they practice beforehand.

500 Nitro