In reply to James1982:
James,
I ran my first marathon last year on 22 Dec and my previous times, mileage and target times were virtually identical to yours.
I printed off the 'Advanced Marathon Training Plan' from the Running Bug website and followed it almost to the letter throughout. The thing I liked about this plan was it measured runs in time rather than distance - i.e. the weekly long run built up from 70 minutes at the start to 2.5 hours at its height. It was a 16 week plan.
Also, aside from the long run, most of the other sessions were very similar to the runs I was already doing routinely (steady runs, tempo intervals, 800m reps etc). The only real difference was the weekly long run, at which I would consciously reduce my pace; I never measured anything, just ran the times required according to the plan. I expect the max distance I ran in training was about 18 miles, but these were quite hilly and on gravel tracks not all road.
I also did loads on the running machine, which I found to be great for anything apart from the long run. Regarding pace, I would always aim to be at 7.30 pace for a steady run on the machine (30-60 mins) as I reckoned that this would equate to 8 min mile pace outside. So I paced carefully inside, but just went with the flow on outdoor runs.
Weekly mileage built from 30 to not more than 55, but mainly about 40-45. All of that enabled me to aim for 8 minute mile pace on the day. This was not quite achieved, but I was not that far off.
For me, fantastic success would have been 3.30, failure would have been 4+. On the day I got 3.41. Based on my experience, your stated plans (pace, mileage, ambition) seem pretty close to what mine were - so entirely realistic.
Finally, listening to your body is admittedly important, but so is the discipline to get out 6 days a week. That's what got me through the last 6 miles!
Good luck,
John.