Like other large urban airports in FSX, you should not expect being able to fly a complex aircraft like the PMDG 747 into Hong Kong with Maxed AI-Traffic, Maxed Display-Settings and complex Weather Themes the same way you fly a GA aircraft over wilderness scenery. Before you purchase, it is recommended that you take a look at FSX's default Hong Kong (VHHX). If you can't achieve a minumum of 30 FPS at the default Hong Kong, your computer is not suited to run this Addon in FSX.
The Hong Kong Installation program comes with several Install-Options disabled by default. The performance difference between default Options disabled and all Options check-marked is quite significant. Note that most of the disabled Options are performance-intense Animations and Effects that you only see under certain conditions. You will not be missing a single 3D building in Hong Kong by not installing these extra Options. The recommended way of installing Hong Kong for FSX is to run the Installer with the default Options first and then check the performance in FSX. If the performance is good on your computer, run the Installer again and select some, but not all the extra Options.
Below find a series of screenshots comparing default FSX with various Fly-HongKong installations. The minimum installation runs as fast as default FSX, while the maximum installation takes a reasonable performance hit considering the extra Effects.
FSX Water. Performance at Hong Kong varies a lot depending on your Water settings. Max 2.X may result in single digit FPS (with 3D building reflections), while on the same computer High 1.X can result in 30 FPS.
Light Bloom will reduce performance at HK by more then half. Our tests show 30 FPS without and 12 FPS with Bloom.
Anti-Alias. Certain types of AA settings in nHancer can result in a severe performance hit at Hong Kong. We highly recommend Multisampling instead of Super or Combined modes.
For more information and recommended FSX Display-Settings see the Hong Kong documentation.