I believe that what you are seeing in both of those videos is the effect of resonance. Undamped steppers running at full steps (no microstepping) suffer from resonance. See this page. I had to set my drivers to, at least, x2 to get smooth running while testing the code that I posted. I usually run x4 to x16 in my applications. Most of the motors that I have resonate at 200 steps/second (full steps), right where your speed is.
So I suggest that you set the drivers to microstepping at x4 (quarter step) and adjust the steps and speeds in the arrays accordingly.
| MS1 | MS2 | MS3 | Microstep Resolution |
|---|---|---|---|
| Low | Low | Low | Full step |
| High | Low | Low | Half step |
| Low | High | Low | Quarter step |
| High | High | Low | Eighth step |
| High | High | High | Sixteenth step |
low is no jumper, high is jumper in place.