There are reports of 10 speed chains lasting only 500 miles. I got 1600 on my last 10x chain. Count your blessings.

A fellow that rides with us has a Shimano 9 speed triple setup, bad back, and spins in the small rings alot. He has 24,000 miles on the original chain!!! and it is not stretched. One of those "they don't make em like they used to stories?"

To the OP. Follow the measurement guidelines and replace as often as it needs to be. Too many factors to say you should replace a chain at X mileage.