While the speedo reads optimistic -- this is common with the sports cars -- the odometer should be real close.

I drove 200 miles in my Boxster after resetting the trip odometer and a GPS and they agreed within 0.1 mile over 200 miles. For a 50K mile warranty that means a 25 mile error in the odometer. And I'm not sure I trust the GPS device to be accurate to within 0.1 miles in 200 miles.