I have flown JNB-IAH in Y, which I think is much better thatn UA E+ and MUC-JNB in J which was business/first on SAA and it was much better than international J on UA/LX/LH ( I was on a J award ticket so SAA leg was in business/first). Service was very good, food was good, lay flat bed was made up nicely with a matress pad, duvet and big pillow Tons of entertainment.

Flown both Y and J on SAA intra-africa (JNB-CPT, JNB-VFA, JNB-POL, ect...) and I am always surprised at a meal service even on a very short flight. J on JNB-CPT surprised me by serving tea in an actual tea cup and saucer, which I think is nice.

I am sure SAA long haul in J will be a pleasant trip for you. Enjoy!