I'm heading out to Australia soon and will be doing a loop that will roughly follow this route: Melbourne - Adelaide - Alice Springs - Darwin - Cairns - Brisbane - Sydney - Melbourne.
I'll be doing it on a 600 thumper also and intend taking in lots of National Parks on the way with as much off-road/tracks as possible (within reason.....it's a big country!) I plan on staying in country for 3 months but might extend if my budget allows.
I'd be more than pleased with some company on the trip, however I'm flying out mid-August as I want to reach the North before the rain comes (we get more than enough of that in the UK, don't you agree???). Anyway if your trip dates are brought forward for any reason let me know. In fact you can get in touch in November as I might still be there!