Also, Java has its incredible reputation for efficient and speedy applets.
</sarcasm>
I know that's not related to JavaFX, and probably not an issue with it either (I can't say; I haven't tried it), but let's face it: Java's not world-famous for being fast client-side, and even if most of its speed issues are a thing of the past, people still perceive it and anything relating to it as slow.
--- Mr. DOS