Thanks Tianci. Was a lot of fun yesterday. I got referred to some doppler software (WaveOsScope) and I may have done it wrong but I got 250.07km/h which is 155.4mph.
Link to WAV file below if anyone else would be kind enough to analyse and tell me how wildly off I am.
http://claregrace.brinkster.net/rc/pass2.wav
EDIT: Chap on RCG reckons it was more 105mph. [

] Never mind.