Sounds like flying in J, in which case domestic leg is also J and BNE-MEL is much more pleasant than SYD-MEL, also immigration/customs at BNE is generally faster and less crowded. Transfer by bus to domestic is also slightly easier, but still needed at BNE. So it isn't just the seat, and the A330 cabin comfort in J is significantly better than the old J on B747s plus there is less chance of breakdown (those B747s were planned to be retired by 2015 in the original fleet plan). So more to this decision than just timing, origin airport and seat "slant". The A330 beds are of course both fully flat and level and have "suite" style.