Ceramic balls were created for ultra high speed use. Yes they are hard but they are also not as tough as steel (little to no ductility as I recall but this knowledge is a bit dated).
What hasn't changed are the physics of the system. At high speeds, the outer raceway sees whatever radial loads are applied PLUS the centrifugal loading of the balls. Thus, ceramic balls (having less mass than a comparably sized steel ball) will generate less centrifugal loading of the raceway. At the astronomical speeds the bearings were asked to run at, large light balls (ceramic) or many more small diameter balls (BNT and BNC style bearings) were the only way this could be achieved.
At 5-6k (within the design window of a typical 2J BPT spindle bearing) ceramic balled bearings will tear a bigger hole in your pocket but not necessarily provide any better value over a traditional bearing. At one time, they were NOT as tolerant of abuse (interupted cuts could cause them to shatter - after all, they are "pottery" to some extent).
Keep in mind that high speed spindles are typically NOT going to see grunt type cutting. They cut with MANY cutting blades rapidly cutting into the material at shallow to moderate cutting depths.
Grunt type spindles have either duplexed, triplex or quad ball bearings at the work end to share the load. In real grunt use, they use tapered rollers or cylindrical rollers to absorb the radial loads from radial milling. A ball thrust deals with axial loads from drilling. Again, this is usually done at lower speeds and heavier loads.
Milling machines can be compared to diesel trucks and F1 engines. The diesels handle the hard grunt work and chug along at low speeds for long periods with little maintenance. F1 needs no explanation.
Bottom line: $peed co$t$ money and time (for maintenance). How fa$t do you want to go and for how long???? Unless your machine was designed from the get go to run at speeds that necessitate, you can bet that retrofitting to ceramics probably won't do that much for you. But they are great to have for the "bling" factor.
And yes, bearing design is a fastidious application of mundane mechanical dynamics, thermodynamics, metallurgy and lubrication engineering.  |