I've considered the JNB-PER as I have friends in both. The problem is that the route is only served by Qantas now (with SAA code share) so there is no competition and I found the cost of a single was prohibitive, particularly in biz! My plan was an RTW but if you return on that route, it might not be a problem.
If you used SA to JNB and then their code share, that might work or the BA and QF share for OneWorld.