The weight on the dumbbells should be challenging, but not impossible. It's mainly there to make those deadlifts a little more difficult, if only to maximize the use of the legs as opposed to the arms. For the mile run, today is the day to try to PR that run. The 400 meter splits will be a good gauge on how to pace it. Negative splits would be good (improving the time every 400 meters) but staying consistent is also a good goal. On that final 200 meters, sprint that sucker.