From my point of view the perfect combo for plains game in Africa is 300 H&H Flanged and 375 H&H Flanged. You can take all game from duiker to eland.
If you are seeking one caliber only I would lean towards 300 H&H Flanged, 8x65RS or alternatively 7x75R vom Hofe.
As you can see I recommend the rimmed cartridges only for reliable extraction.

CZ hunter