Torque doesn't decrease with speed, Power does. Torque remains constant (at least in an ideal world, but there may be a slight variance due to things never being ideal).
And torque is directly proportional to current.

The only way you're likely to kill an induction motor with adequate cooling at rated speeds, is by pushing too much current through the windings, which can cause them to overheat. Even though the spindle is water cooled, heat transfer won't be ideal, so by pushing too much current, you can still overheat the windings.
Torque boost options simply increase the current. For short boosts it's not likely to be a problem, but prolonged it is.

For this kind of application, I would be monitoring the motor current, as that will give you the best indication of just how much load you're putting on the motor.