If you're running 9:30-9:55/mile well below MAF, you will easily
be able to break 4 hours, as long as you put in sufficient training
mileage. When you finish a run at that heart rate, do you feel
"unsatisfied," as if you hardly did anything and you could keep
Run like a kid again!
I agree with Jesse. I think you should be fine as long as you get those long runs in during your training.
I'm still trying to figure out the whole heart rate thing though.
One thing i will note is that Maffetone does allow you to add 5 beats to your time if you've been running regularly (3-4 times a week)...of course 155 would be your high number with a zone of 145-155. It's best to try to stay as close to the lower number at the beginning and end of your run, allowing it to ramp up in the middle.