Claas & hay

After NH time I have now a jag -08 870. Equipment list says there is a v12 chopping cylinder 4-17mm. I think 17mm is very short and I´d like to do longer chop. Claas has v20, v24 and v36 drums. What idea? Only for maize? My friend said rock stop works better when feed rollers rolls slowly. So, do I have to take some knives away for doing longer chop and keeping rockstop at work? At NH FX I had 6 knives and chop lenght was 30mm. That was what I´m looking for. Sorry my bad english. :/

Claas & hay