bear, Derg:
the grease is not a solution - keep in mind that the bearings need cooling which comes from the flow of cooling medium - in this case oil or oil mist (depending on load/speed). So the best idea to get better cooling is to make sure the bearing will get more oil mist or cooler oil mist. On the other hand there are some Trent9xx engines working relatively long time so there is a lot of examples supporting tha case that thereis a technical possibility to achieve this.
Ball bearings are made to tight tolerances and than are selected to make sure that the balls within one bearing are almost the same dimension to achieve that there is always a lot of balls to carry the axial load (the radial load is always carried by limited number but due to high bearing diameter and elastic deformation of the balls and the raceway it would be always more than one. The manufacturing and selection tolerances are really tight - some measuring equipment mentioned in the docmenets suggested has accuracy of 2nm so i may safely assume that selection may be carried into groups with tolerances in region of 20nm. That is really precise and we may safely assume that the balls are practically equal in size. The other problem are the raceways which can not be selected but have to be preisely machined, than precisely assembled and then they behave the way the mounting itself. And the dimensional changes here are several times bigger than in the bearing itself. No wonder the design here is demanding and critical to bearing longevity.
And the further the splines are from bearing plane the shorter their life span is. Sometimes critically short.