A 50 mile bread & butter week for me would look something like this:
Long run (x1): 2:15, easy (usually 4:45-4:55 pace depending on terrain)
Medium runs (x2): 1 @ 1:30, mostly easy with some hill reps (ie 8x1min) or shorter intervals (ie 3x4min) or just using terrain to vary intensity; 1 @ 1:30, mostly easy with the middle 3rd at tempo (or upcoming race pace, if any)
Short runs (x3): 2 @ 0:45, both easy (around 5:00+/- pace); 1 @ 0:10, easy transition run
Total: 6:55, or around 85km (53 miles) give or take.
I'm not advocating you do this, just sayin' ('cos you asked)... What mileage did you see signinficant gains?
By averaging 80.4km per week (almost 50 miles precisely), min 40, max 100, over a period of 26 weeks this past off-season.
blood, sweat...and big gears
I hated every minute of training, but I said, ''Don't quit. Suffer now and live the rest of your life as a champion.''
- Muhammad Ali