All those calibers you mention are fast and will blow holes if you hit bone or a full rumen on a little guy with an expanding bullet. But go with a tough bonded or tsx and aim behind the shoulder on litelevision guys.
Too bad on bushbuck, leave gemsbuck oryx for Namibia unless you see a real whopper. Forget lechwe from your list as you mentioned, expensive and easy hunt in the EC. And I would leave blue wildebeest for Limpopo or another indigenous area.
If you want a tough hunt, vaal rhebok and klipspringer. But you may not have enough days. Mountain reedbuck is fun and usually reasonable. Steenbok and duiker are challenging enough. But you will have to insist as not high priced and often seen as oppertunty animal by PH'S.
Zebra or red hartebeest and black Wildebeest are great options! Black Wildebeest in the right open areas and herded up are fun and challenging. Just picking out the best trophy is tricky. Then they will run inot a figure 8 to make a cloud of dust, then run out the other side and over the next hill.
How in the hell did an animal evolve to throw smoke grenades to cover their retreat? Hahaha