For once it sounds like the media may have got the terminology correct - it would normally be the propeller on the back of the aircraft that was turning. The overhead rotor would not normally be rotating during a taxi. The rpm driven by the Rotax would be anywhere between around 1,500 to 5000 +, depending upon where the throttle was set. Prop diam is around 1.73 m, so you can do the math if you want. 200 mph is a good way for a prosecuting brief to indicate the hazard, I suppose. The linear velocity close to the root is much less of course.