Hi ric_melb,
When I did the CBR-SYD-HBA-MEL-CBR run on 4 December, two flights were on a 737-400 and two were on a 737-800. I can't remember which way round it was, but the SYD-HBA-MEL was the same aircraft.
Yesterday, the SYD-HBA-MEL-CBR was a 737-400; I think, but I don't recall exactly...