Firstly, Welcome to the Network & the Forums tlc.

Most carriers will be heavy out of Oz 5-9 Dec as they are the last few days of low season airfares before High season kicks in. A lot of people get out for Xmas and the suchlike at the cheaper fare levels.
That's not to say you won't get on, but you will find things very heavily booked for the most part. Looks like JD may have given you the skinny on QF loads over those dates already.
Cheers.