I know the word on the street is that stock F10 M5s are limited at 155, but no say about 6MT.
Aside from BMS Stage 1 tune (which doesn't de-limit our cars), resonator delete and charcoal filter delete... the car is completely stock. Didn't get a chance to go into 6th gear either, that was at top of 5th (as you can tell the car is telling me to go into 6th).
Have a video if interested....