Need to get to Boston, need help (Page 2)

Without a doubt a marathon run to the best of your ability will take something out of you.  It will also compromise your training in other dimensions.  First, the taper costs your running volume and the recovery further costs you.  A couple of years ago I was able to have enough discipline to hold back and just go hard enough to drop below 3:10 so I could later do Boston with a friend who had qualified for a first time after many attempts.  I did not wish to take too much time out of my training longer term.  I did this and recovered quickly (though my true objective was to BQ with a 3:20), my point being it is very hard to hold back.  I think you can do a marathon with a 90%, perhaps even 95%, effort and minimize the taper and the recovery.  It is the push to the limit that gets you.  A marathon run to its limit will without a doubt cost your overall training by a month to one and a half months.  If your IM is six months out it may not be a big deal.  I would not do it within the last two to three months.  I do not think it is possible without compromising your IM results.