I have a image that is 10000x6800 in a ImageView the frame rate drops to 3fps. At with:

 Image contextImage = new Image(
                App.class.getResource("images/Render4k.png").toExternalForm(),
                4096,4096,true,true);

It goes back to 55fps. Seems like this should not be that slow. at 5000px wide its 48-53fps.