Mickey made some very good points here so I think there is little more one can contribute!

At the risk of sounding dry - and not wanting to create an encyclopaedic atmosphere

- I'll refer to some weapons used by some better known cullers.
Mickey Norton I believe only used a .375H&H so it ought to be quite good.
The .404 Jeffery had a thoroughly good reputation being the issue rifle of many countries.
Some of the most experienced cullers went for the .416 Rigby.
I don't recollect any names but certainly many also have been quoted using doubles so I suppose it's not excluded by any means.
However, considering the large number of elephant to be shot in one go, the magazine certainly makes a good case for itself.

Referring to Tony Sanchez-Arino's views I'd exclude the .375 in this case (and not wanting to pretend any more knowledgeable or smarter or better than e.g. M. Norton!) and go for something a tad larger.
My choice would probably be the .404 on the following grounds:
- powerful enough, excellent penetration
- large mag capacity
- low(ish) recoil

The last point counting out the .458 Lott fir me; and probably the .416 as well. Plus that the .416 Rigby cartridge is so darn big that it reduces the magazine capacity.

- Larry