Australian domestic or international?
More so got to do with your status with QF, esp on international flights.
Classes, whY, flexY, J, or F (where offered) only gives you earnings as to FF mileage.
The higher the fare, the more FF points you earn.
Plus now that you can bid for an upgrade, so your class you bought for, not much placed on that, because the more $ a person who has bid to go up a class, from Y to J or J to F, the more chances that person has to the J or F seat than you, if you did not bid for the upgrade.
Some on here do not accept differences of opinions, drivel its called.
But you can work it out for yourself, now that bidding has come into play.