Another idea: take into account the movement of the mouse to define a directional cone in the general direction of the movement, which would enable you to preload your pages even before the hover state occurs.
I've always hated menu dropdowns where it would close if you try to skip to the next submenu you've opened, since you hovered on the other parts on your way to the submenu.
So you'd end up having to perfectly 'trace' the menu so it won't close down on you.
The coolest approach given was when a user types in the search box, kick off the request for the full results page if they move their mouse on a motion curve towards one of the results, with some machine learned data on how people move their mouse: Not quite in a straight line, and with some acceleration.
<link rel="prefetch" href="http://example.com/page2" />
edit: @devgutt else already mentioned this. I had this page open for a while before posting.
The actual HTML is only going to add another few KB.
But caching the skeleton of the page will work. We need browser to do it for us, just like browsers already caches the images.