Andja, although the speed limit for both these bearings is in the range of 3800 RPM for grease, I have been suggesting to my customers that they look at an SMA Air/Oil system from Dropsa. It has taken many applications and extended the life on these bearings by as much as 6 times over what they were getting.
If you dont want to change, I would suggest looking at your grease and running at least an EP1 in the same product that you are currently using. If you compare the two greases you will see that the base oil viscosity in both products should be the same, however the EP1 has less thickener so it will flow better. Although you may not be using an automated system, and the better pumpability is not an issue, you have to look at the fact that an EP2 may be causing viscous drag. It certainly won't harm anything to try the EP1, but it may help you.
Dean