This depends on the motor, the load on the motor, and the control gains/algorithm.
With the included 64 in-oz NEMA 17 motor, reasonable PID tuning, in closed loop velocity or position mode, speeds of over 300 rpm are easily reached (unloaded). The key to reaching higher speeds is careful controller tuning and adding a phase advance. We have implemented phase advance code, but haven't played with it too much. Without too much tuning we were able to get speeds closer to 1000 rpm.