Not much of one. If there is it is so minimal that it doesn't interfere with the browsing experience. And when I just browsed through several pages to check it I've got 6 Safari tabs open and Outlook is downloading 17,000 emails. Not the heaviest use by any means, but a reflection of my typical use.Not sure what the difference is. Maybe the very subtle delay that I wouldn't have noticed if I hadn't gone looking for it is not so subtle to you.