For hunting dangerous game in South Africa the 375 Holland & Holland is the minimum caliber prescribed by law. The 375 Holland & Holland is also the minimum caliber required for dangerous game especially for Elephant and Buffalo in most other African countries. Zimbabwe however still allows the 9.3 x 62 Mauser and the 9.3 x 64 Brenneke to be legally used for Dangerous game hunting. The 375 Holland & Holland is the most widely used 375 but authorities will also allow the new 375 Ruger, the 375 Remington Ultra Magnum as well as the big boy among the 375’s the 375 Weatherby Magnum to be used on the Big Five. Please note do not even consider using a 375 Winchester on any of Africa’s Big Five, it is not only illegal but you might end up getting killed by your intended target.
I would advise against a first time hunter to Africa using a caliber like the 460 Weatherby Magnum or the 505 Gibbs, not because these calibers aren’t good for hunting the Big Five, but purely and simply because there are very few individuals who can shoot these calibers accurately without flinching. The recoil of the 460 Weatherby Magnum and the 505 Gibbs are substantial and very few people will want to put in the hours of practice from the bench required to become proficient with these rifles.
Always use the best premium quality bullets for hunting dangerous game in Africa. The African Big Five game animals are notoriously tough so please do not try to save money by using cheap ammunition, it can ruin a great safari and even cost you your life. When hunting dangerous game like Elephant use the best monolithic solids available. When hunting Buffalo it is recommended that you use premium quality expanding bullets like Barnes X for body shots into the vitals, but if you have to follow a wounded Cape buffalo and risk facing a charge make sure you also have some good monolithic solids on hand.
So as far as your choice of rifles and calibers it’s up to you what you bring with, just make sure it is legal to use. Also make 100% sure that you can consistently shoot accurately with that particular rifle from shooting sticks and various field positions. Practice your shooting on the range and do some research on shot placement by reading or watching footage on shot placement. There are good books and videos available by Kevin Robertson, a veterinarian and professional hunter who has made a detailed study on this subject. Remember the more you practice your shooting skills the more rewarding your hunt will be.