Cheers Minni / Fiona - it would make sense to me that a higher mileage program is better preparation, but according to this article there are veteran marathon runners who have knocked minutes off their PB after switching to the FIRST/'less is more' program:
http://www.runnersworld.com/article/0,7120,s6-238-244-255-8257-0,00.html
interesting reading!