questioner of reasoning wrote:
Right, but 1:22 is a terrible time for a 4:10 guy. I'm not trying to insult you - it's pretty good for after ten years off and for only running 30 miles a week, and you have every reason to be happy with it - but it's really not good evidence that 28 mpw is sufficient volume for racing well at distances over 5k. If you'd run 1:08, you'd have a point.
If no cross training is allowed, I think the mile is the best bet for an endurance oriented person (maybe 3k or 5k in extreme cases, but I'm skeptical) and anything down to 60m depending on how speed oriented you are.
The problem when this question comes up is that, ultimately, everyone assumes that a runner wants to run elite times off of 28 miles per week. Sure, you won't pop a 13:45 5k or go to the Olympic trials, but you might be able to enter your local 5k and win at least your age group in 17:30 or go run a 4:35 mile.
The standard for what is "good enough" performance-wise is highly subjective. If you can realize 90% of your potential off of this training, is it really worth the several extra miles each week to realize that last 10% of potential? For some people it is, but for others it is not.