The most significant increase in speed will be obtained by using a quality oil lubricant. Bearings are not meant to be opened and re-lubricated as the different types of lubricant may be incompatible and it also leads to the possibility of letting in contaminants. So if you want to try oiled bearings, you should use bearings that come ready lubricated with oil from the factory. It is important to note that oiled bearings will become damaged much more quickly than greased bearings.
We sell various types of greased or oiled bearings in our online store.
If you would like to ignore the warnings and experiment with your own lubricants, we sell packs of 608 bearings with snap in non contact seals and no lubricant (factory clean).
Some suggestions to try
Note! These types of product do not offer any protection once the liquid lubricant has been fully expelled from the bearing, and your bearings will become damaged quickly. If you do decide to experiment with different oils it is important to try to keep the bearings lubricated.