Originally Posted by
Yaks
If you're aiming for 3:30 ( 8 min/mile ) then I wouldn't be doing any sections of my long runs at 6:45 - 7:00 pace.
The plan I follow has myweekly long run alternating weeks between at 10-20% slower than target pace, and progressive ( but progressive from the slower pace up to marathon pace, but not any faster ).
If you can do some miles at 6:45 - 7:00 at end of a long run, then ( with all other appropriate training ) then I'd say you were on for nearer 3 than 3:30. Depends though how much other mileage you are doing during the week. The plan I'm following has me running 6 days a week, including a medium length mid-week of about 12-15, so already quite tired at start of a Sunday long run. If you're fresher at start of run, then easier to knock out a decent pace.
Unwritten rule that is often quoted is to try and get your 5 longest runs to be at least 100 miles, ie averaging 20 miles. Say building up 18, 19, 20, 21, 22
Good luck !