Gievn the apparent hen's teeth nature of South Africa then my sights move to Hawaii.

Blue would get 18,097 (7239 miles x 0.25 for WT+)
Silver would get 21,717
Gold would get 25,337 (surplus of 337 miles!)

I havent priced the flight but it is a long time to be sleeping on a flat bed compared with the six and a bit to JFK. Good use of miles I'd say.