If it's this same 600C
then it says that it can't have it's speed limit set any higher.
If it has an option for "off" you could try that. The manual doesn't show this available, but...
It does also have a section
that appears to be saying that if if t his setting is off, it should work all the way up, otherwise it only works up to the assist level's limit. But it doesn't specify if the max limit in 8.3.1 is still obeyed. (presumably, yes).
Some other thoughts:
Is the wheel diameter set correctly, so that it is reading the correct wheel speed?
Is the speed signal for the display coming from a wheel sensor with a single pole (magnet), or from the BR?
If from the BR, is it from a single pole wheelspeed sensor, or a multipole, or from the motor hall sensors?
Depending on the above, you may be able to change the settings or the sensor input or the sensor itself to change the actual speed sensed by the display so it does not attempt to limit. But the displayed speed will be wrong.