Save your money and go with the standard metal shield bearings.
You can buy alot more of them for the same $ and replace them as often as you feel like.
Metal shield bearing are a none contact seal and spin freely.
Rubber shield bearings are a contact type seal and do not spin as free as the metal.
The clutch bearings are small enough that the any weight savings from using ceramic are minute.
There is also another site to concider, Avid Rc Bearings have what they call a revolution bearing it has a rubber seal on one side metal on the other.
They have them in ceramic as well as metal, I like them because you can remove the rubber seal easily, clean, re-oil and replace the seal.
However whatever your choice you should be fine as I think they all last about the same.
Mugen MRX4X - Novarossi
Nuggets Ranch Raceway
Byrons - Xceed