Want to start a brushless speed demon.

[suicideneil]

Break? no.

Its just a safe limit since thats what most bearings are rated for, in theory you can swap the bearings over for something better/ higher spec/ smoother etc and that wont be an issue anymore. The main issue really is that BL motors are most efficient in the 30-40k rpm range, so the higher past that you go, the hotter the motor and esc will tend to run. Its also an issue with the rotor, since not many companies wrap it with anything (like CF or kevlar), so the magnets can fly apart at very high rpms- not such an issue with small motors, but your typcial 1/8 motor is more susceptible.