are the loads to JNB bad? if not, you'd be best served to take DL to JNB, overnight nearby at chain hotel or homestay and zed to CPT next day (or late eve flight to CPT). Pending your seniority, you might get better service w/upgrade on DL. That's a really long flight from AMS in coach--what's your gateway? I can check some SA flights via my ASU membership. There are never any guarantees, of course. And I think we have KL person here.
What's your departure date?