What is the movement rate of a falling creature or object each round?


This question assumes that no method of controlling speed or direction is available, and that the falling is taking place from a location 30′ higher than necessary in order for said creature or object to reach the maximum falling damage of 20d6. The fall occurs from said height, proceeds directly, and impacts the ground of solid rock at the resulting velocity.

Thus, what is the movement rate of said falling creature or object each round?