Limited by my meshing skill and my laptop performance, I have to assume Rarity's body is a cylinder with a length of 1.5 m(5/3 times pony's height), and diameter of 0.5 m. The coefficient of drag of such geometry is about 0.18+_0.02. Assume her weight is 110+_20 kg, the equilibrium velocity should be 120+_20 m/s
Before the equilibrium, Rarity has fallen more than 5160 m, If there was no ground, she should have fallen for 51.6 s. Actually, the time duration is only 49+_1 s, the distance she traveled is only about 4800m. Rarity's initial position from the ground is only 3 times of the height of the stadium, comparing to the error in the calculation, it is negligible. Her final position can also be regarded as 0 meter from the ground.
∴The altitude of Cloudsdale is around 4800 meter.