I use a Garmin 500 when I race. But when I am racing, I don't look at it. One - it is too distracting to me (and I have 8 fields displayed so trying to find what I am looking for in a hypoxic state doesn't work), and two, I know it is typically a 40 minute race, but I go by lap count instead.

I analyze the data after the race when I download it to my computer/Strava.

SheFly