Remember the speedo is wrong. The climatronics and GPS usually tie in.
But the Climatronic display takes its readings from the wheel speed sensors, and not GPS (as reported on other forums) - because only cars with factory fit sat navs will have a GPS antenna.
Mine is just over 130 mph on the mountain circuit IOM. Which, for that road, is slow.
How many miles have you done in your car? Most cars will get faster as they get more miles on the clock.
Anyway, saw just under 145 on the clock in Germany with about 3k miles on the clock. Was sooooo tempted to take it round Assen too.