Greg,
I was amazed at Kruger. If you can work an overnight stay there, that would be awesome to go on one of the night game rides. Everybody has to be OUT or in one of the protected compounds at closing time there. I was able to see the Big 5 there. Both cats not very impressive. Rhino, Ele, and Buff most impressive in that order to me. The size of the park is incredible.
If you stay in Joberg at all, try to eat downtown at a restaraunt called Kreme. Best food I have ever had...including your cheesy potatoes!