It's really interesting! We had a long discussion about speedo error and many people claimed 5-10% ! I also saw a letter from BMW that up to 10% error is normal and dealer will not touch the car in that range to make correction.
Now, this video... according to BMWUSA, at 6th gear the gear ratio is 0.84 and the rear axle ratio is 3.15. With 295/30/20 tire at 7000 RPM, M6 is able to reach 212 mph (~340km/h)... looks like the speedo is pretty accurate (2% off)...
http://www.dragtimes.com/gear-ratio-...tton=Calculate
Anyways, nice to see M6 can reach that speed
