The product is substantially the same in J on all aircraft, but as stated earlier there is some chance of getting a flat-bed A330 which do fly MEL-SYD as repositioning (not sure if they ever fly SYD-MEL though). Maybe QF does some maintenance work on them in MEL, in any case I am running over 50% flat-bed A330s for MEL-SYD in the past few months (out of about 10 flights) and zero SYD-MEL. The 737 service is better in J if you are in the first row and I do prefer it to A330. But food/drinks are identical and there isn't time to play with the flat bed too much so not really a comfort factor.