Hello
It looks like your DRV8825 stepper motor driver carrier is not one of ours. That board might be configured differently, so that might account for the difference in the behavior of the nEN pin.
By the way, I forgot to mention this in my last response, but it looks like the datasheet for your 0.6A stepper motor has a pull out torque curve in it. You can use that as a rough estimate of the types of speeds that motor is capable of. If you want more advice about getting stepper motors to step quickly, you might find this forum post interesting.
Grant