I did the MBJ~KIN in 1989 as the route was: LGW~BDA (IIRC)~MBJ~KIN.
In a BD Saab (I forget the model number) there was DND~EDI which I clocked at 11 minutes wheels to wheels and we could see EDI almost as soon as we lifted off. That was 1998.
With regards to JNB to ORD and over water, I have not done the route but I thnk SAA transists at Abuja or similar in West Africa. I sit to be corrected.