PO is one thing to concider but I have read that the JNB employees sometimes do not want to deal with DL standby's (its not DL empl. down there, I think S.A.A. deals with the DL flight)
backup would be 1st KLM to AMS then BA or VA to LHR, as these flights leave after the Delta flight.
Still trying to determine if vacation days needed is worth time spent in CPT (more vacation time needed than days spent in CPT) Coworker is heading down for a quick trip and I am tempted to join.