As somone who has successfully redeemed OnePass miles for JFK-LAX-MEL-SYD-LAX-JFK in QF FC, I can tell you the following.
QF allocates 2 FC seats per flight (usually). There are many posts of people successfully getting two. There are at least 4 BC class seats per flight, again many posts.
You MUST look on the QF site and book at least 330 days out. The QF FF folks get first dibs between 360 and 330 days out. Thus, they snap up most of the available seats, ESPECIALLY those around the holidays. I would say that a non-QF member's chance of a free seat at that time of the year as virtually zero.
After the QF folks are done, at about 330 days, then CO, US, AA and others enter the fray for the leftovers. It is not impossible, just diffficult and you need a looooog time horizon.
Its still the best use of OnePass miles out there.