DRZZ400S: 40 HP (29.2 kW)) @ 7600 RPM
You should set your (safe) red line just above the RPM where you have max. power i.e. 8,000RPM - 8,500RPM
Can't find figures for the "faster DRZ400E motor but it does make power a tad further up.
I don't think it's clever to set it much higher than 9,000RPM for a roller bearing crank of the size used in the DRZ unless you're happy with frequent crank rebuilds.