Some more detail...
I drove up from Austin today and had some time to test it. Once again, the digital readout on the cockpit display looks to be accurate, the "analog" dial is fast. I first noticed it when I set the cruise control, so I switched my Passport 9500i to speed display (great gizmo, btw). Matched the digital readout. I then broke out my trusty Garmin Nuvi, it showed the same.