Ignoring deviations for area winds with which I am not familiar, then the maximum southerly latitude of the GC route between SYD and JNB is 50deg 43 mins. This occurs at long 95deg.
The Antarctic coastline through here (Australian dependency) has the edge of the continent proper is about 66S. If that was in the north, then it would be half way down norway!
That still puts you almost 1000 miles from the edge of the landmass.
Jetstreams might force you a bit closer, but not for too long I would think.
CS