Shane..I owe u $20 from the drag day - pm me u details!
I have used a navman and Garmin on my yacht as a speedo, to compare the actual speed and VMG (which is another speed reading for yacht racing) againsta my actual instruments. It read clsoe if not the same and they cost like $5000 for all the bits and pieces.
In the car I use the TomTom 710 as stated before. Yeah unsealed roads anrt the best however I have never needed to use that feture. The big touch screen is really good when driving and very easy to read. My wife can use it (thats why I bought it) and she reckons its ace, press the "home button" and it directs you straight home. I just had a look in it I notice key points of intrest are CHadstone, Chapel Street, High Point and the QV CarPark. LOL sorry at home beating of..