Has any member been thinking on, or even tried to remove the speed limiter DYI? It is common to calibrate bikes speedo meter after change of gearings by a so called Speedohealer.
http://www.pashnit.com/product/speedohealer.html
It may perhaps be possible to fool the 335i ECU the car is running e.g. 10 % slower than it does, thus raising the top speed by 10%?