The problem with all of this tough guy talk of 140mpw, is that most people are in reality running "up to 140mpw" leaving the impression that they are running 140s regularly. Also, when you are putting in that kind of roadwork you NEED to come down off of it periodically. Listen to your body.
I'd not recommend 2:20 marathoners to put in that kind of mileage. It would be better for their ultimate development if they work on becoming a better runner in the 105-120 range first before going any higher. Only after making that 2:20 breakthrough (or similar track or road time) would I dare to give the green light to 20 miles a day.
I've done 120-145 a week in college, in fact i did it during the racing season, undefeated and breaking the course record on every course. It shocked a few of my friends (All-Americans) to learn later that I had put in 20 miles the day before most of those races. But I set myself up for it, getting almost all of my credits finished in three years, making it easy to manage my schedule.
A stress fracture in late March limited my training. I ran my first steeplechase on May 30th, but came back two weeks later with an AR at nationals. The first thing that my coach said to me was "all of the mileage in the fall really paid off big." No kidding.
Again, if you are inclined to try to bump it up that high you should listen to your body closely.