I train on a Dura Ace 12/25 cassette. I am averaging about 5k miles before shifting gets choppy. I replace my chain every 1,500 - 2k miles. Does that sound about right based on what others are getting out of their DA cassette / chain? BTW, I race Cat 3 and train a hard 150 - 175 miles a week with a lot of intervals, so those are not easy miles with smooth shifts every time, but I do my best to keep things smooth as much as possible.