If you have the time flexibility and the patience to wait for scarce award seats, I'd shoot for a Oneworld award - ORD-xLHR-oCPT-oJNB-xSYD-xHKG-xNRT-ORD or some other RTW route. If you only stop over in SA and transit through the other cities, it would come in at around 18K miles, or the OW180F award level, 20K miles less than the partner award between N. America and Africa. That way you could use BA F to JNB or CPT and QF F to Sydney, then JL or CX or AA F back across the Pacific, assuming no QF F award seats could be had.