I would go against the advice of the overwhelming majority of PHs if I did not agree that the .375 H&H is the best all round caliber for African hunting.
I have a .375 for the plains game,kudu,sable antelope and gemsbok.
However since Cape buffalo is the only game on the menu I would prefer not to use the minimum legal caliber.
If I were hunting only leopard I would use a 30-06.