BTW I am not a big fan of the race predictors. I only bring it up because you mentioned your 5k time. It can be fun to look at, and can be a measure of fitness, but if you ask me it has nothing to do with a marathon. For example I have run a 19:40 5K and a 41:40 10K (both in the last 9 months) and according to McMillan that should make a something like a 3:15 marathoner. It doesn't and I am not. In fact, I am not even close. My advice (crappy advice as it may be) is to trust in what you have learned from your experience, trust in the massive amount of training you have done, and use those to gauge your goal. Pace predictors are fun, experience will tell you the truth.
Agree to an extent. However, it seems like Mike is gauging his readiness for his goal marathon time based on experience, not on the calculators. With the amount of experience Mike has, I have a feeling he knows what kind of 5K time he has to run before he's ready for a 3:20 marathon.