If you are looking for fast and effective breaking in this circumstance i would look more to better calipers and bigger disks.
My suggestion is Genuine discs and pads. More than enough for motorway mileage.
Go for the B5 or B6 S4 calipers + discs upgrade, relatively cheap to do and will definately give you more stopping power.
Straight swap!!...
Check out: http://www.a4mods.com/index.php?page=webcontent/pages/b5s4.html&category=2