do not do 35-40 miles a week for base if you're training for the 800. that is, of course, if you are not a sprint based 800 runner. im assuming that you are either an 800m specialist or distance based 800 guy and 35-40 at a decent pace is not the way to go. for right now just build up milage and dont worry about pace...once u hit ur peak milage for the summer throw in some tempos or fartleks 1 or mayb 2 times a week but dont even touch the track. you dont need to do any intervals until about 1 month before you start racing the 8, and even then i would do more strenght based work like 800s or at the lowest 400s. the 150s are actually a good thing, however, to keep good turnover throughout the summer.
running slow does not take away from your speed...not running fast does and these strides will keep you fast.