Full throttle up. With the DJI Inspire 1, the max speed is about 22 m/s which translates into about 50 mph. Fast for a drone! So you can have your drone keep up with a car if you need it to.

The max ascent speed is 5 m/s and the max descent speed is 4 m/s.
https://youtu.be/SNPmLb-4pA8