Difference between MAF Training and marathon race pace?

When racing a marathon, it appears those with the most success run at a pace just faster than their MAF—about 10-15 seconds per mile faster than your MAF pace.

I base this on those who I've trained and who are healthy and fit. An unhealthy or unfit athlete will have to compensate for their problem—by running with too high a heart rate, for example, thereby not achieving their best performance.