Streching is for the most part pointless (its one of those odd theories that doesnt apply so much to modern day athletic science), and its been proven use google (you dont see lance armstrong streching his legs out before a race, you see him on a bike turning the pedals over to warm them up, he dosent strech!). Just do a short warm up jog or some sort of warm up excersizes for the muslces your going to use, so they are not in shock when full load is placed upon them. Also Im not sure why every one thinks streching is so crucial...Last time i checked streching never helped my endurence, or speed for that matter. Make note i have done two miles in 10:58 which is nothing to brag about, and never did i stretch for any of it Every one has differnt muscle make ups so you may be more fast twich then slow...Theres a lot of factors.
I do tri-athealons so i know some stuff, and your best bet is to vary your training (repetition is good to a point). Do one mile one day as fast as you can go, something like two miles the next at a steady pace, rest, repeat. Also take caffiene pre workouts, it will help WAY more then it will hinder. And finally SUFFER, you can olny push to threshold, but I am sure you have not done this, because you have not collasped, which is a miserable feeling, being it has bappened to me. keep pushing and good luck.