Q: How low do these actually drop the Model S?

Ride height is adjustable anywhere from stock height down to 60mm lower than stock. Because you set it mechanically on the coilover, you pick the exact stance and corner balance you want and it stays put, which matters on a track where consistent ride height affects handling. Going lower changes geometry, so plan an alignment, and add the adjustable rear camber arms if you want to correct camber at the new height.