@mijostyn said "The air bearing does absolutely nothing to alleviate the high horizontal mass, that would be magic. "
I understand- I guess, from my crude understanding of mechanics/physics, this is the difference between "weight" and "mass,"- that is, while the air bearing, properly designed to account for the load (of the entire arm "carriage") will relieve the weight or friction between the arm tube and the travel rail, the mass of the carriage remains the same.