
I recall on the first trip my car simply stopped accelerating at 166mph (GPS) (Numbers were still increasing relatively quickly given the speed before this happened) It then flickered between 166 and 167 for the next 5 mins, before traffic interupted play. Once through the traffic, the car accelerated back in exactly the same manner to 166 / 167 mph. Seem to recall it beign bang on 7K rpm in 6th. This has pretty much been repeated on subsequent trips.
Each fast Germany trip has (co-incidently) been on pretty worn 275/30 tyres, (as opposed to non fast trips on speed limited winter tyres) which have a slightly smaller rolling diameter than the standard fit 255/35's. This may account for any variations in the max GPS speed seen.