I've read that on B6s at least, the speedometer is calibrated to always show slightly higher than actual speed. (See link below)

If so, is there a setting that could be modified using VAG-COM to disable that "feature" or modify it?<ul><li><a href="http://forums.audiworld.com/a4gen2/msgs/283688.phtml">http://forums.audiworld.com/a4gen2/msgs/283688.phtml</a</li></ul>

Are you running stock wheels and tires? Changing the size of wheel and/or tires will result in a difference on the speedo.

Speedo/Trip computer and GPS. The speedo reads higher than the trip computer which reads higher than the GPS Approx 5-7% difference btwn the speedo and GPS. My B5 S4 is bang on all three so I assume it's the Avant. My dealer has had a couple of complaints on this and is checking to see if there is a fix. I'm running 16" for winter right now and will check again when I put the Summer 17"s on in about three weeks.
Hugh

and I am currently running on my 16" winter set, which uses the OEM size.

But keep in mind, the trip computer's average speed computation closely matches the actual speed, while the speedometer is off. This seems to indicate a problem with the speedometer reading itself.