Can't offer you much advise except

1. I don't think you can upgrade the ZED, at least not on CX
2. Don't fly when its close to end of the month as Chinese New Year starts from 26 Jan 09 and loads to HK will be extremely heavy especially few days before 25th (i.e. everyone needs to be home by 25th). This holiday period will last at least a week or 2. Actually you can aim to fly on 26th Jan, which is new years day where no one will be flying (just like flying on Christmas day itself)

Let me know if you have any other things about HK you want to know. GL