I did the exact hunt you speak of with Roger the first ten days of this month. You will love it! I took a .458 lott and a .375 ruger. I asked the same question you are asking and found that I would be encountering some cheeky elephants in the valley and Humani as well. I opted for that combination and kept a couple of 300 grain solids in the bottom of the magazine of the .375 ruger. It worked very well. I used .300 grain Swift A-Frames for zebra, wildebeast, kudu, warthog, and impala. I used the .458 for the buffalo and a big bull hippo I took on an island in the Zambezi. I used 500 grain A-Frames and Hornady 500 grains solids. Be sure to get a firm commitment on the area you will be hunting and the PH that will be guiding you. You will probably hunt the valley for your buffalo and then go down to Humani for plains game. Its a good way to experience two hunts in one. Humani is a zoo. You will see alot of game there. You may have one PH in the valley and another in Humani. That worked well for me, but I would like to know the game plan in advance. Roger and Anne are very nice people. So are Sarah and Guy. Good luck! Bottom line: I think a second rifle should be capable of stopping dangerous game if animals of that description are present.