I'm an 800/1600 runner (junior in high school) and i run around 45-50 mpw. How effective would running a moderate 3-5 miles before school be if i did it once or twice a week? I'm guessing im in 4:30-35 shape for 1600 and 2 flat shape for the 8. Given it's still quite early in the indoor season and not wanting to burn out or plateau, would it be a good idea to start doing 1-2 doubles a week?