You're pretty much assured that your A330 flight will be new economy, as that's the type of aircraft which CX operate almost exclusively on Australian routes. If your flight is showing 33B this denotes the new configuration aircraft, although as always, there is no guarantee as there can always be last minute aircraft substitutions.

As for the A340 flight, if your flight is showing 34B then that reflects the new configuration aircraft. Note that CX have only in the past week or so announced that they are withdrawing some of their A340s from service due to the downturn in travel, so it's quite possible that they will substitute an A330 to operate this flight.

Hope this helps.