That calculation seems to be a good tool based on people I know with those 5k prs.
AreYouWithMeSoFar? : using a 5:10 mile pace , the easy run pace comes out as about 7:10 with this calculation. I think this seems like a good number, probably better than my original suggestion of sub 7 pace, and better than running 8 min pace.
I worry a little about americans thinking they can train with lots of slow mileage. I myself am a fairly high mileage advocate, but I also think that the quality needs to be progressivly built up along with the mileage. It is easy to get ahead of yourself by either: running too slow and too much, or too fast and not enough. I think elite american runners just need to train smart, thats all. A lot of this is by feel, of course, which means going as fast as you can on "base building", distance, or easy days without over-reaching, or taxing the body more than it can recover.
The energy systems should be kept in mind : learn to get the most out of the aeribic system on aerobic days by staying CLOSER but NOT OVER the lactate threashold. *If you never get near your lactate threashold, then you are actually neglecting a huge part of aerbic system, which i assume is the opposite intention of running a high volume program.*
I hope you have a great upcoming season and some big PRS. GOOD LUCK!