It depends (of course). First of all, markup wise page content can take only a small part of the whole page HTML. Navigation, widgets, etc. can be substantial.

It depends (of course). First of all, markup wise page content can take only a small part of the whole page HTML. Navigation, widgets, etc. can be substantial. Also, you'd want Expires, not Cache control. Otherwise you may end sending dozens of request just to get 304 back. Keeping that in mind, sending single AJAX request which delivers _only_ content seems quite beneficial compared to full refresh scenario.