Jo'berg flights rarely got much further than 62-63. As Going Boeing mentions below, SCL flights go down as far as 71.5 Sth. The charters occasionally approach 75 South but that's about the limit as there's plenty to see (weather permitting) between Cape Hallett and Terra Nova Bay without having to go any further South. The alternative is a westbound run across to Casey station, in which case you won't get much more than 67 South.

The return flights from SCL to SYD frequently go as far as S71 30.0 The area further South hasn’t been charted to the required standards and there is some terrain which could affect the depressurisation requirements.

Lucky enough, the first time that ETOPS-330 approval was given to a four-engined aircraft.