I was going to suggest the 270 grain loads, but there is nothing wrong with zimhunter's suggestion. The thinking being that you want a little more velocity than you would get with the 300gr if you are in more open country like parts of Namibia. Eland and zebra are very tough, but a 270 grain .375 would be perfect IMHO, although you won't get much expansion on the duiker!

By the way, where are you going to find tommys?