The 60CSx is an excellent choice, IMO. Yes, it records all the fitness data that the Forerunner does except for heart rate. You'd need one of the many stand-alone HR monitors in addition. Many PC programs can analyze the recorded track log and report the usual fitness numbers, most more completely than the Forerunner by itself.
The Forerunner is very specialized and good at its intended use, but not at all the best for auto and boat: no maps! Plan to buy the nautical charts and highway maps that load into the 60CSx. They are not cheap unless you think of the cost per state or per mile of shoreline .
I use the older 60CS (looks the same, but less memory and less sensitivity) and find it excellent for biking and hiking, adequate for auto.
The 76CSx is almost identical internally but has a larger case that floats; it is advertised for nautical use. Both units meet the same waterproof spec: IPX7. Unfortunately for cycling, Garmin's handlebar mount positions the 76CSx where many peoples' knees hit it. One can mitigate that by buying another brand of mount or a handlebar extension, but both add weight.
As you might guess, this is a popular topic here. Browse the group for more opinions. Also, the General Discussion group has a thread "Not finding the ideal GPS for cycling" starting Jan 4, 2006 that is relevant.
Fred