There was a recent article in Runner's World Magazine about what distance race best suited you (http://www.runnersworld.com/article/0,7120,s6-238-244--13007-0,00.html).
The quiz results confirmed that I am best suited for the middle distance. I also realized, however, that training with the stroller best supports that distance (8-13 mile races). While I have strapped a child into the stroller to do 20-mile training runs, I was also just a little lucky that her temperament was suited to that sort of thing and I don't know if I have it in me to push the double jogger for 20 miles. On the other side of things, it is nearly impossible to keep the same posture and biomechanics one would need for sprinting when you are pushing a stroller. So watch out 10-milers! Here I (we) come!