What I've never quite understood, is how you can go from max 20-22 mile runs at 'marathon pace' plus 45 secs to 1 min per mile, to doing 26 miles at a significantly faster pace, having never experienced this in training? Of course, the atmosphere on the day will push you further, etc, but should you not attempt a 'mock' marathon performance at least once beforehand, even if it takes a fair bit out of you and requires a week or 10 days of rest/light training?