I had to take a break in the middle of the second five-minute run-- after about three minutes of it, my heart rate hit a point that was a little higher than I'm comfortable with. I walked for a bit to get my heart rate down, then finished then run. It all turned out fine, and I probably could have finished out the last two minutes without a break, but pushing it didn't seem like the right idea.
Even if it didn't go quite the way I wanted, this run allowed me to establish a plan. I'm going to set up shop in W4 and stay there, while slowly increasing my pace until I get to where I want to be.