Setting the damper on 10 is a good way to hurt yourself if you're a smaller guy or if your form isn't perfect. Probably won't happen on a 500m, but I wouldn't want to do it for a 2K. Also keep in mind that damper settings can vary from rower to rower and are affected by temperature, humidity, amount of dust in the fan, etc. so finding the drag factor at a particular damper setting is a far more useful standard to go by.
(WFS) was started by a former competitive rower and should answer all your questions.