Source: Flyer
The records are:
1 Speed over a 3km course, in an aircraft with a take-off weight of 500kg to 1000kg: 337.5km/h. The pilot was Walter Extra.
2 Speed over a 3km course, in an aircraft with a take-off weight of 1000kg-1750kg: 342.86km/h. The pilot was Walter Kampsmann (GER), an aerobatics pilot.