According to my calculations, each wave in the Infinity Tower in Cat Quest III takes exactly 3 seconds if you somehow manage to spawnkill every enemy.
Every time you clear a wave, the tower goes 1km down. So each wave takes 3 seconds to go 1km down. 1km/3 seconds=20km/min=1200km/hour.
Mach 1 is 1234.8 km/h, so the top speed of the Infinity Tower is about 35 km/h slower than sound.