It can extrude 3mm filament at 35 mm/sec, faster speeds will require a more powerful motor. I am using a 4.4 kg-cm stepper powered at 1.3 Amps.
The vertical clearance is kept to a minimum so taller objects can be printed. Not shown in the pictures, but a 40 mm fan is to be mounted in front of the extruder motor.
Sample video: http://youtu.be/Kf_FaiNjeag