Trust me, I have dealt many times with QF about QF108 availability and sometimes have had to buy F as there was no way to get A (and QF does guarantee seat on oversold flights to WPs, but not in A). You might get lucky, but without QF status this particular flight is difficult in both A and D (other QF flights are much easier). Month end and quarter end are particularly bad, so I guess the date of your flight also affects the chances a fair bit. But be aware that QF108 has special yield rules (due to extensive F and J last-minute travel between JFK and SYD due to certain Australian companies having split operations between these cities).