Indianapolis, near a mall and not a lot of time, so I didn't experiment outside, maybe Sunday. I went next door to a Bally's, forgot my iPod and ran looking out the window, suffering to an episode of Maury. I ran for 10 min at 6.2mph, jumped to 8 for 2 minutes and felt good, so after a minute at 6.2 again, I went to 7.0, then back to 6.2 before cooling down.
I checked my heart rate when I was halfway into the 7 and it was 172, then when I dropped from 6.2 to 4 it was down to 147, then 133 a minute later. Not too bad.