Skateboard Bearings Ceramic vs. Steel

Skateboard speed relies on many factors, the most important one is the RPM (revolution per minute) rate of the "Ball Bearings". The ball bearing consist of inner race, outer race, balls, balls retainer and optional closures.
As you may all know, any skateboard has 4 wheels (DUH), each wheel has 2 ball bearings, makes them all 8 Ball bearings, and they are (of course) sold as a set of 8 ball bearings. RPM of the ball bearings relies on reducing the friction between all the moving elements, here are the factors affecting the RPM:

1- Quality: The quality of any bearings are classified by the American Bearing Manufacturers Association ABMA as ABEC rating, the more the ABEC rating the more precise bearings were manufactured, or tighter in tolerance; in other words, the most common and good choice ABEC rating is ABEC-7.

2- Inner and outer race material: Carbon, chrome, zirconia and stainless steel are your options. For regular skate, I wouldn't choose anything but the Chrome Steel, well .. this is the widest used bearings steel. However, if you go to a race or a skate compition, you better sacrifice cash and go for the zirconia

3- Balls material: Again the bottom line is to reduce friction, your options are (sorted best to "not bad") silicon nitride ceramic, Zirconia ceramic and steel.

4- Retainer material: Your options are (sorted best to "not bad") zirconia, PTFE, bakelite, nylon, bronze and steel.

5- Lubrication: I suggest just any multi-purpose oil, since a skate-boarder can always take good care of his hardware, grease will make your wheels hard to free-spin

6- Closures: used to protect the moving parts of your ball bearings from outside contamination. If you are skate-boarding in a perfect environment (there is no such thing) with no dirt, no water and no humidity then you can always use your ball bearings without closures. Your options are (sorted best to "not bad") Teflon seals, metal shields, non-contact rubber seals, and contact rubber seals.
Confusing, Huh?, I am sure it is. Fortunately, any of the above selections should be good for regular skate-boarding, for professional skating go for the following good choice:

8 ABEC-7 Skateboard Bearings:Ceramic:Sealed:Nylon Cage

VXB Ball Bearings