I have been 15 times and used nearly every option for Africa.
For plains game - 280 Rem to .300 WM
For dangerous game - .375 HH
If only taking one rifle - .375 HH
Better yet, rent a rifle from your outfit or PH. I have done that on most hunts. Cheaper in the long run. Easier traveling as well....
Forget the days of taking your own rifle unless you will spend an extra $400 to $1000 to take your own gun....