I would strongly recommend the .30-06 with that favourite load. On your list Gemsbok is the toughest animal you will hunt.

The .30-06 is about ideal with a premium 165 and will have the range if you are challenged by Springbok. You will also need something very accurate if you are hunting duiker and springbok at longer ranges. An accurate .30-06 will give you confidence and you will also have more of a chance to watch your shot impact with the .30 cal rather than the .375. (Something I find very satisfying.)