Brian,
John Purdey has a very serious point.
When I was a young RAF Officer in the mid 1960's; every Airfield with even a medium sized Town near it was expected to put on an Open Day for the Battle of Britain anniversary.
One of the great "standby's" was the "Guess the height and speed of the aircraft" as a single aircraft flew acros the airfield at a predetermined height and speed.
In my experience nobody, of the general public, got within 30-40 kts and 2-300ft.
The point is that ones conclusions as to height and speed can be prejudiced by ones previous experience with aircraft of different shape and size.
Mr Holbrook may well be correct; but NO tests were carried out to assess his peceptions in relation to height and speed in relation to the Chinook.
If PSO to CAS is reading this then maybe you could arrange a trial?