In my experience the prices at Hong Kong airport duty free weren't particuarly special, especially in relation to Sydney airport (I last passed through in December, and the exchange rate was about the same as it is now). Given you can buy alcohol on return now anyway, it might be worth your while checking out the prices when you're departing Australia, then compare them when you land at HKG - if they're looking good buy them then, otherwise wait till you return (and at least if you buy on arrival you don't have to lug it all around Europe with you ).