When to sell?

I just picked up an 04 X2 about 2 months ago. It just hit 170hrs today, and will definitely have 300 by the end of the year.

At what point do the hours start to significantly affect(effect?) the resale value of the boat? If I keep it all next summer, it would be 800hrs+ by the end of October. I've seen 12 year old boats with fewer hours.

The boat still looks/performs like it has 20 hours, but I know a high hour reading will scare away most buyers.

I believe I could sell the boat in the fall, or next spring and only take a 4-6K hit on the resale. The question is, how much money will I lose if I keep it all next summer and put 800hrs+ on it?