I don't know about the particle size of the other fillers other than the iron oxide. But, I am very satisfied with the 110 product iron oxide from Kremer. The same goes for the 0.3 micron Chromium Oxide from Kremer.
I contacted a representative from Kremer with the same question about the 0.3 micron CrO. It took them a week to contact the technical staff in Germany and get an answer. Basically, they said that the QA on the product was extremely stringent. And, that they couldn't guarantee that bigger particles didn't exist. But, if so, they would be a very very small percentage.
I would suspect the same applies to other Kremer products. Anyone I have heard talk about Kremer, and most seem to be European, speak very highly of their products.