How close is McMillan calculator (HM to Mary)

Recent thread on McMillan here:

http://beginnertriathlete.com/discussion/forums/thread-view.asp?tid=469514&posts=28&start=1

But yes- if you bank the miles and the training, you CAN run a 3:13 full.  The 3:13 is what your body is capable of in ideal conditions.  Start taking minutes off for environment (hot or cold), altitude, elevation change (i.e. hills), wind (can be significant), and sub-optimal execution.  Execution requires perfect pacing, hydration and nutrition.  Keep in mind, for every second you go out too fast in the early miles, add 2 seconds to the later ones.  Unfortunately the reverse isn't quite true.  If you go out a second/mi too slow in the early miles, you don't get to run 2sec/mi faster in the later ones- so this is where Mcmillan is useful.  It let's you know how you can pace to achieve a more optimal overall time.  As any time spent above threshold, even a little, is very damaging.  

Planning on going out slow and negative splitting is a 'safer' way to run the marathon, but not an optimal way.  

Keep in mind- that to achieve McMillan- it's gonna' hurt.  A LOT.  It's the limit of what your body is capable of.  Shooting for a 3:13 and failing may yield a 3:40.  Shooting for a 3:30, is much more likely to yield a 3:30- if that makes any sense.  

Slight correction here: it is what some bodies are capable of in ideal conditions. Most people don't reach their McMillan equivalents for a marathon. Probably in most cases it's due to insufficient training. But it's also relevant that some folks are better suited to shorter distances.

I find McMillan to be pretty accurate for distances up to HM, but that it's too optimistic for Mary distances, perhaps by about 5-6 minutes in my case.