I've got no specifics on this, but would dare saying that a GUI library is the least of your worries when it comes to speed-optimizing your app... If you have lots of GUI controllers, it will help though to split/group them thematically into tabs, so when it comes to rendering them every frame, only a small subset needs to be drawn. The same thinking will also apply to event handling inside CP5. If you have 100 controllers in total, but only 20 in the currently active tab, then these are the only ones which will receive the event and check it.