I’ve visited the link so I can return there now at any time myself. Looks great in Firefox with smooth scrolling but IE has a few issues. One is that the size of the laptop looks too large. Windows 7 IE 11 here. I suspect the lagging is caused by the exact issue I described earlier. Other browsers with an instantaneous response (as opposed to a smooth scroll) to the mousewheel will fire a
scroll event with no delay. But IE takes about 70ms to react, then fires the event afterwards.
Not much time right now but I’ll check again later.