I'm just wondering if there's really (actually two) a (ball) bearing in an air spindle? Or there's no ball bearings, instead there's "air" bearings, that cushion the pressurized air, and "floats" inside the rotor, and there's never a contact between the rotor and the housing. And since the bearing friction is some orders of magnitude bigger than a ball bearing, the air bearing can easily self-destruct with centrifugal force.
I have been many many times using with the dental drill. Current drills can operate at up to 800,000 rpm, but usually 400,000 rpm works fine. The torque is not much, but the interesting thing is their absence of vibration.