Link: Good article, thanks! I'll add to my library on bearing issues. I could definitely see, that with a plastic or soft metal cage, there may be less wear than balls sliding against each other in opposite directions, which is what happens between loose balls. However, more balls helps, and I think in an application with low rotation, like headset, loose balls may be ideal, unless, as you said, the cages do not reduce the number of balls at all, or little. It's notable that bike hubs use loose balls, as there are few balls, and cages might reduce that even further. Cup and cone bottom brackets, typically had metal cages, and high radial load, and I think benefited from loose ball with more balls, a number of bike authorities have said that. Preload is critical for good durability on hubs and BBs, I have discovered.