In the open configuration (without cover glass) the droplets can go really fast. So in the video below I ran some speed tests. Three droplets are moving in a small circle, in a big circle and in a linear up and down movement. See what happens.
Measured speed: 80mm/second or 35us/step
PS: I found that small droplets can even go much faster in one direction. They then just miss the corner or the turning point and slide of the array.