There's a big difference between running by yourself and running with another person. When you run a long and easy by yourself, you will only go so fast because you're taking it easy. When you run with another person, you push yourself and go a lot faster than you would have gone alone. I read in one of Sean Covey's book "7 Habits of Highly Effective Teens" (back when I was a teen) that when geese fly in formation, they fly 71% further than they would if they had gone alone. There's that, but when running with another individual, you not only have the competition, but you also have the encouragement that automatically comes with running together.
My next race is going to be the Nashville Rock 'n' Roll Marathon on April 28th, and I want to race well, so my plan is to get my mileage down the next few weeks, and then after 3-4 weeks, work on both speed and endurance. Let's see how well training is going to be!