Just my two cents...as a guy who has ran consistently in the 17's for the past two years.
1. 50 mpw should do it. I run with a couple older runners who run in the 17's and they have absolutely no wheels and they top off around 50 AT THE MOST.
2. Make sure you are doing every type of speed workout.
One week do hard hill reps and a 4-5 mile tempo later in the week. During the tempo, tell yourself "this is not a race". My tempos when I was running 17:30 were always around 6:00-6:10 pace. Sometimes they were almost 6:20.
The next week do long intervals (1000m-1600m) with 400m jog rests, and hard track workouts of 200's-400's with equal recovery later in the week. Sometimes you need to train like an 800m runner. Don't be afraid of these workouts. Get tough.
The next week do a combination of long and short intervals (ladder workouts), and then later in the week a road fartlek.
Constantly CHALLENGE your body and trick it. Giving your body new stimulus promotes growth.
3. LONG RUN. Don't neglect it. 10 mile long runs don't cut it....but 13-16 milers do.
4. Run by feel for your easy mileage...DO NOT look at your watch until the run is OVER. Don't be depressed if some of your runs at end up being 8:15-8:20 pace. Even Cam Levins has 8-minute pace days. You should do whatever feels good on those filler miles of 40 minutes or more.