If you have a classical desktop interface where you reach 100+ widgets (which sounds like a lot but is easily reachable with just a toolbar, some buttons and a form), the difference is noticeable when interacting even on recent hardware (i5+).<p>For example, since I work in visualization, I often tie data widgets to the GL canvas in order to provide realtime feedback. I also use Qt5 in order to provide keyboard accelerators. With QT5 the rendering latency grew so high that I couldn&#x27;t provide realtime feedback anymore, and I had to batch requests (and finally reverted to Qt4).<p>Incidentally Qt5 widgets can be used in a GL context directly, but are way too slow to render and manage events to be used consistently at 60 fps (they&#x27;re not designed for that, so their scope in this sense is not as broad as it can really be). It&#x27;s actually faster to give them their own GL context in order not to interfere with your pipeline, which kinds-of defeat the point.<p>I&#x27;ve also found that the additional JS glue doesn&#x27;t provide any benefit unless you go <i>entirely</i> QML.