I did some additional Doppler checks and the best I could come up with was 142 mph. I compared it to a f3d video I have that looked faster and Doppler had it at 160+ mph. I did notice the Doppler sound lines went off the top and bottom of the chart at an angle that is a little unusual.
Edit - I usually wait for someone to ask for a Doppler check but with the title of this thread I could not resist. Below is a Doppler check of the video listed above. I do not know what type of airplane it is. Some assume it is a Q40 but I chose not to assume anything. I have been using Doppler for some time to determine speed of RC aircraft and it has been varified many times with radar and other methods. This reading was very easy to read but I guess it could be wrong. I also came up with 25,000+ rpm, is that about right for this engine?
Here is the f3d video to compare Doppler and just watching. To me it seems noticably faster and is close to 170 mph.
http://www.youtube.com/watch?v=Km-l5s6T4aI