In order to find his speed, we just need to compare the distance that Mineta moved and the distance the whip moved in one frame.
Mineta's Height = 108 cm
Mineta's Movement = 0.34 m
Whip's Movement = 0.35 m
The tip of a whip travels at twice the speed of sound (Mach 2, 686 m/s). However, for this feat we are using the loop of the whip, which travels twice as slower as the tip (Mach 1, 343 m/s). This is the part of the whip that creates that characteristic sound, which we can hear in Mineta's scene.
Timeframe = 0.35/343 = 0.0010204081632653 seconds
Speed = 0.34/0.0010204081632653 = 333.20 m/s
Mineta's Speed = 333.20 m/s, Mach 0.97 (Transonic)
The distance he moved was very short and to the sideways, so this will be classified as a combat speed feat.