I still plan to keep to headway speed even when we're more than 600' from shore until the lake level comes close to the normal full level. I too saw many wakes traveling much farther than 600'. Friends of mine in Alton Bay had quite a bit of damage done to their dock by wakes generated by boats more than 600 feet from the shore.
It wouldn't surprise me to find that the piece of dock shown in RG's picture belonged to them!