OK, not planning on there being much response here, but I figured I might get lucky. Its a bit long, but bear with me if you will.
First some background. In HS, I was an above average runner at anything from the 400 through XC. Never great, but pretty solid all the way around, did a max of about 35 mpw, lots of intervals, not many of them longer than 600m. 1:58, 4:37, 9:53, ~16:30 5k XC.
In College, I slowly worked up my mileage to the point where I was hitting between 85 and 100 pretty consistently for long stretches. More emphasis on tempo runs of all varieties, long (800m+) intervals at various paces, and long runs, with some basic speed thrown on top. Ended up running 3:54, 14:45 and a 9:11 steeple. No great marks in XC though, PR at 8k is 25:35, which is the basis of my main question.
Ended my college career by injuring myself at conference, which was a little under 18 months ago now. After about 8 months I started running haphazardly again. I wouldn't call it training because every time I got about 2 weeks into a good groove, I would re-aggravate the injury. Maxed out at about 50 mpw a couple of times, but over the last year, I have probably averaged in the 20mpw range, mostly 3-5 days a week, mostly easy runs with some harder workouts thrown in to keep from getting too out of shape.
Recently, I have been feeling much better and I decided to give racing another shot. I send about a month getting ready for an XC race (on the same course that I hold my 8k XC PR), during which I ran weeks of 36, 22, 39, 39 miles. I didn't run too many workouts in this period; the best workout I had was 4X1200m at LT Pace (3:57, 3:57, 3:55, 3:54) with 1 min jog rest. In those 4 weeks, the quality work I did was 4 workouts, all less than 5k in duration.
At the race, I figured that given my condition I could reasonably expect to run 28:00 on a good day. I ended up running 27:11 after holding myself back for the first 3 miles of the race. I was totally dumbfounded as to how I had run a (gasp) halfway respectable race off of such low mileage.
Now to the heart of the question. I am not in good shape right now. When I ran a 25:35 on the exact same course, I was in awesome shape (5k time trial was around 15:25 at that point, during an 87 mile week). Course was in the same condition, I was not, and yet I managed to run a better time than I did when I was a College Soph logging 80-90 mile weeks consistently. Am I a low mileage kind of guy? obviously, I was in much better shape logging consistent 90 mile weeks, but could I have been overworking myself? Would I be just as well off running 70s as running 90s.