"The
speed of sound is the distance traveled per unit time by a
sound wave propagating through an
elastic medium. In dry
air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s; 1,236 km/h; 768 mph; 667 kn), or a kilometre in 2.914 s or a mile in 4.689 s."
Just to clear up the technicalities.
Regardless thats a wee bit fast. Fastest speeds in Bleach I would say is around the region of 80-140 mph, or 120-250 kmh.
This can be counted with various battles namely Soifon vs Yoruchi.
80 mph is most likely.
Now before that is scoffed at, the fastest human on record moves at 27 mph. And in Theory a human that unlocked all barriers and was willing to cause harm to themselves ending in death likely, as may be the case with the Legend of the Marathon, that was 40 mph.
So 80-140 is well, pretty fast for a human, or human like being, not even most animals reach that.
As to how I reached that math.
In this fight among who could be considered the fastest combatants in the bleach universe, its rather easy with size and for sure fixed distances to judge speed and time. Given most of the rapid in close movements happend within the blink of an eye, thats .4 seceonds.
Speed plus time, well there you go. But given the shaky nature of bleach my math could be off and might should even be ignored. The point is, no one in bleach even while falling has reached speeds greater than terminal velocity.