1000 movements
In 2009, HKG ranked 41st busiest among the world's airports by aircraft movements. In 2010, HKG was still not ranked in the top 30. Granted, the primarily wide-body traffic explains some of this. For passenger traffic, HKG ranked 11th in 2010.
However, with better ATC these numbers could be improved by some margin. That should be the first priority, but the politically incorrect reality is that it will take many more gweilos to get the job done and that is not going to happen.
So a third runway becomes the next viable option, but how much does it really accomplish when there is still only one departure and arrival corridor, especially considering the previous point about ATC.