Hi Paul,
I think you are doing too many hard sessions each week. You say that you run 'hard 2-3 days each week' as well as doing one leg weights session as well!!
I was in that boat too. Simply loved training hard!! But you will halt improvement, theres just not enough recovery.
I'd Keep the long weekly run, but make sure it is at 'easy' pace. McMillan calculator will let you know the correct 'easy' pace based on your 39 min 10K pace. This will look after your aerobic capacity (20 miles is a bit overkill for 10K though. I max out at 14-15 miles in the long run). Your other 5-6 mile runs are fine too, but I wouldn't do them faster than 'steady' pace. 'Easy' pace would be fine for these too.
Now, the real business in bringing your 10K time down will be in devoting just two days a week to hard work. Keeping at least two easy days between each hard session. I rotate speed work, hill reps, shorter distance race pace time trials and longer distance tempo runs.
After getting to a 39 min 10K, for speedwork I worked my way upto 12 x 1/4 miles at 75 sec pace with a 1:30 recovery. On the half mile front I worked up to 8 x 2:50, again with a 1:30 recovery and on the mile reps 4 x 5:55 with a 1 min recovery.
Every other week or so I would attempt a 4 mile race pace time trial until I was under 24 mins.
The Hill work was every couple of weeks (1:30 reps and jog back) for 13 mins. I did this twice in the middle of an easy run.
Tempo runs were basically 40 min 10K runs. But at your stage right now a 41-42 mins 10K would be fine.
As for your gym sessions, I'd say that they'd count as a hard day that would require two days of easy running or a rest day for recovery. I tend to do my squats and hamstring presses every couple of weeks, just to make sure I'm not losing strength.
I dropped my 10k from 39:08 (April 2011) to 37:10 (March 2012) doing just this. I'm 33 years old, but I'd imagine your development wouldn't be much slower with the same training. Weekly mileage varied between 25 and 50 miles a week. 35 would probably be my average over this time.
I'm sure you'll be successful with the right approach. Do your hard sessions hard, but only twice weekly. The rest of your running should be pretty easy mileage based.
Good luck
Edited: 09/08/2012 at 22:40