I have a dura-ace 10 spd chain with probably 6000 miles on it. From what I've heard that is a LOT of mileage for a DA10. But I check it with a park cc-3 chain checker and it measures fine. I swap out an old and a new cassette without a problem fairly often. Should I change it or just keep on measuring until it shows enough stretch? Most folks I know get much less mileage out of a DA10 chain.