Like you said this is the one the that SPA has they say it will go to 999.9 mph. This one uses a magnet that you can place on whatever you want, wheel , drive shaft, pulley....
http://www.spatechnique.com/product_...eedometers.asp
Just want to see all my options before getting one.
I have also heard about using a km/h and just slowing down the cable to that is is mph.