Running 100-120 miles a week makes you tired. You won't run anything near a PR while running that much. Too much muscle damage, legs are tired, your stride is just short. In terms of progression and adaptation think of a huge general macro cycle in which your fitness drops because you are running hard and running a lot of mileage but then once you taper and reduce the mileage your fitness jumps way up and you're able to race much faster than if you didn't do the high volume and hard work. So think of many micro cycles within a much larger macro cycle. You have the day to day micro cycles: races hard, train hard, easy runs, etc and a much larger macro cycle: this year, next year, year after that. This is IF you're still putting in the heavy volume. If you wanted to race well in October then you shouldn't be running peak volume or anything near peak volume. The poster said he was 80-90 during the summer, 100+ in August and still in the 100s now...that's peak volume on top of peak intensity. He's not overtrained, he's properly trained and will roll in the next few weeks if he drops the bottom out of the mileage but maintains the intensity, I'm sure his coach knows this.
Alan