@pindac , thank you for those links. Very interesting, especially moisin’s comments.
@rauliruegas , I appreciate your experience in this matter, as in others analog. Is it that you think the ruby material (actually sapphire, as it turns out) has a preferable sound to the Si3N4? I ask because the hardness and density of the two materials seem virtually the same, which means their friction and stiction will be pretty close to each other when the bearings are unflawed, which means their mechanical performance should be pretty much the same. So what’s left? Whence your strong preference for ruby?