A motor will only go as fast as you have volts to apply (with no loading taken into consideration), so whilst you can run a DC motor and its drive at below its rated voltaged, the maximum speed possible will reduce. This can usually be calculated from a motors RPM/V specification and this will typically be specified with no load on the motor. Many motor drives will have a a voltage drop across them, maybe as much as 5%, reducing the voltage the motor itself finally gets.
1 vs 4 Quadrant Drives
A 1 quadrant drive can't decelerate quickly and handle regenerative loads (when the motor is being pushed by the load). If your application is on a cam or such like loading then you will often need a 4 quadrant drive which will control regenerative loads better.