In motorcycle racing, we've change wheel bearings and transmission bearings. But we didn't replace the bearings with coated bearings. We used ceramic bearings.
The ceramic portion applies to the ball, not the races.
Here's what I know. A ceramic ball has a uniform size and shape. Additionally, its surface topography is very smooth. Its Rockwell hardness is more than a steel ball, and when it's loaded up, it doesn't deflect like a steel ball does.
When set up in the races, they can use tighter clearances and a lighter grease as they are uniform and don't expand like a steel ball because of deflection and heat. They will outlast a steel ball bearing under the same conditions. They are lighter.
So, in real world applications, what did we see? People I knew in drag racing found that they could gain an extra 2-4MPH in a quarter mile. Adding about 4MPH to a 150+ pass for some. In transmission applications, specifically some Buell's that use Harley-Davidson engines, a lot of internal "chatter" was reduced from the transmission shafts being able to remain more in their fixed locations. Some use them in steering head locations, which isn't a fast rotating area, but the lack of ball deflection made steering input easier and consistent all the time. Take a motorcycle wheel that has ceramic bearings and just rotate it on the axle with a spin by hand, it rotates longer that one with a regular bearing.
I haven't seen those kind of results with treated bearings. I think that's related to the fact that it is still a steel ball.
Ceramic wheel bearings for a motorcycle are usually around $400+. Usuallly, you'll try to do that toward the last thing on your set up.
The guys I go to for answers are
here. You'd call them, they aren't big in email.