The POWER (Watts) required by a fan varies approximately (theoretically) as the third power of the speed. Therefore, increasing the speed by only 10% increases the power requirement by 1.1 cubed = 1.331; or an increase of 33 percent. Since power= Volts x Amps, that means you need 33% more Amps.
Now resistive heat loss in the windings varies as current squared x resistance. The resistance is approximately constant, (actually increases slightly with temperature), so the heating increases as Amps squared, or 1.33 squared = 1.77. That means that a 10% increase in speed will increase the heating in the windings by 77%.
If you increase the heating in the windings by 77% you will eventually cause failure of the insulation of the windings. That will produce a short circuit - much sparks and smoke - until it (you hope) trips the circuit breaker.
Now, you are the one to decide if you really want to increase the speed of the fan motor.