Again... If you weren't using GPS, but going by the speedo, you are mistaken. BMW vehicle speed as measured by the OBC, and ECU is very accurate where the speedo isn't. The faster you go the more optimistic the speedo is. To verify this, reset the OBC speed function or use GPS, and compare it to the speedo.
At 100+ I've seen some cars differ by 10 mph.
No matter where you go, there you are.