At peak times it wont be worth much, because half or more of the passengers will be Elite/Gold/Koru. This is my experience of QF domestic priority boarding in Oz. A peak time A330 takes a while to board, but the queues for priority boarding can be long in themselves and QF lets both queues board at the same time. Dual boarding OTOH basically delivers most of the benefits, as most priority customers will be in the Space+ front half anyway and the remainder in the rear.