I own, use and love my .500 Jeffery, but I think you need to decide what you plan to use the rifle for. If it's general African hunting then (IMO) the .416 or .404 make a better choice than the .500s. The .500s are absolutely tremendous short range charge stoppers but they do have appreciably more bullet drop than either of the other two calibres I mentioned.

Don't think it's impossible to take a long shot with a .500 - it's not, but it's a damn sight easier with a .416 etc......

If of course, you primarily want a charge stopper or you're pretty damn sure you'll only shoot it at closeish range or a rifle to shoot just for fun, then the .500s would be a better choice...... Hell, just buy one of each!