Where in Aus are you looking? It's a huge continent. I lived in Canberra (near ANU) for 3 months and was able to get out once or twice a week, but nothing higher than class 4, at least during the winter season, which is when I was there. There's definitely some good stuff up north near Townsville also.
I've heard Tasmania had some sweet boating and some harder stuff as well.
check out Paddle Australia - The interactive guide to Australian paddling...
, it has runs in Tas and all the other territories as well.