See section 3 (style the header links) in the original post. I arrived at 13px.
Best advice to anyone trying to customize this header... learn to use Firebug (or the Chrome equivalent). F12 brings it up. Inspect what's already there, you can tweak it in real time, try and learn how it works. If you can make it happen in Firebug, then copy those changes into your own CSS sheet, and it will work there too.