HTML5 is fine but unfortunatelly the performance may be very different depending on browser, system, or hardware.
On Mac, and I have the latest iMac 27 there is a large difference between the browsers.
Firefox is superior with very smooth panning even in a full browser window and in fullscreen.
Chrome is much better than Safari but still not perfectly smooth.
Safari is awful. The panning hesitates at around 100 pixels stops, with windows large than about 1400 pixels width.
However in fullsceen it behaves much better but not as smooth as Firefox.
Is there the same differences on Windows between the 3 main browsers?
This is one of my latesst tours for testing. http://360-foto.dk/portrait-now/
Hans