I like trying to hold the same time for the 200s even though the rest descends. Great for testing you execution and making sure you don't go out too fast.

warm up: 400, 3x 100, 3x (kick 2x 25, swim 50)

4x 200 w/ 20 sec rest, pull 200 easy
4x 200 w/ 15 sec rest, pull 300 easy
4x 200 w/ 10 sec rest, pull 400 easy