I flew SAA back in January ATL-CPT-JNB-VFA-JNB-SID-ATL. They were awesome! Even the CPT-JNB leg on the 738 had a hot breakfast. The 732 to VFA was refurbished really nice and had a nice box lunch. And then the long flights on the 744, rivals the world's finest. You won't be disappointed.
On the JFK-JNB leg expect a marathon! I am curious as to how many movies they would show in coach. I suspect that flight is 16-18 hours, on DFW-KIX there was 5 movies shown in coach (I was in first ) and that was 14 hours.