Hatari,

I've not hunted ele or hippo with any of the calibers you listed. I have hunted buffalo and a host of other big game with the 505 Gibbs and 500 AHR though. I agree 110% with the comments made by the other gentlemen on this thread though, in that all the cartridges you named will kill just as effectively IF you place the appropriate bullet in the appropriate place. It is important to understand that all these cartridges can easily destroy an inappropriate bullet.

So my two cents worth is.

1.) Use the appropriate bullet (solids of a premium nature I should think)
2.) Place the bullet in the appropriate place.
3.) Only use one of those shoulder held artillery peices IF you can accurately do so ie be proficient. Otherwise, there are several "lesser" cartridges that will also work.

Scott