In-between temperatures and sizes

[Tortuga68]

Layering...

In additon to your suit, get some undergarments and/or a hooded vest. Fourth Element Thermocline and Sharkskin | Technical Water Sport Garments | Australia and New Zealand are both very good

For me I would use them under a good quality 5mm when diving in & around Port Philip Bay - YMMV

IMO you can feel too hot, both in & out of the water

 

[Murf-Diver]

There is a new 7mm Pinnacle Tempo out just this week. I would seriously have a look at that before going with the 6.5mm Scubapro Nova Scotia. The Pinnacle is made in your neck of the woods so you should get it at a good price. Its important that a suit fits you well so I would also consider travelling to a good shop to try a few on.
I dived in the Red Sea recently in a Nova Scotia at 21-22oC and i was cold on the 2nd and 3rd dives, plus the scotia does not dry our between dives, so its a b**ch to get back into when wet. Apparently the Merino in the Pinnacle does not have this problem.