Hello together,

perhaps http://teethgrinder.co.uk/open-flash-chart-2/ will solve some performance leaks during the rendering of the charts.
With openflash-charts it's possible to let the client render the graphs. The Php Library only generates a special File, and the flash-client makes all the rendering stuff.

Piwik.org is using this library and many people like this type of interaktive graphs.

best regards
Kay Strobach