Choosing a marathon goal time

The past few days I've been thinking about what my time goal should be for the marathon.  Qualifying for Boston is way beyond my current abilities. (I'd have to run a 3:10) Qualifying for the JFK 50 miler is a possibility, but not something I'm very interested in at this point (C standard is a 4:30 marathon)  Going for a PR is always a good idea, but I don't think that would be a great goal this year because it wouldn't force me to work very hard (I would need to beat 5:49:06)  I could choose a round number time like under 5 hours, or 4:30 but it seems a little silly because those round numbers are just picked arbitrarily.

What I want to do is to run as hard as I can for 26.2 miles and finish having nothing left in the tank with the knowledge that I can do no better then what I just did.  On the surface it seems like an easy goal to achieve.  All I would need to do is run as hard as I can until I cross the finish line.  If you've ever started a run too fast you know what a horrible idea that plan would be.  Jacked up at the start of the race I could keep up with the elites for maybe up to a mile, after that I would be in for 25 miles of misery having exhausted myself way to early.  On the other hand I could walk 26 miles and sprint the last hundred feet or so.  I'd have a better time then if I started off too fast, but this still wouldn't be the rewarding experience I'm looking for.  I need to find that magical pace where I'm working hard the entire way without burning out too soon.  To complicate matters I can't just go off of the pace I've been training at.  Tapering a few weeks before the marathon ensures you arrive at the starting line in peak physical fitness.  I will be capable of much more then I've been doing each week on the long run.  Additionally I've found in the past that I thrive on the energy of the crowd and can push myself harder during an event then I can when training.

With all of these factors, how can I come up with a goal? In part by looking back at what I'm capable of.  Last fall I ran a solid half marathon.  It was paced fairly well and was a true indication of what I could do.  Using this as a starting point for calculating a marathon goal time should work well, assuming my fitness is at a similar level to what it was last fall.  That introduces another problem of how do I know my fitness level is similar?  Rick suggested I compare similar runs from last fall and this spring.  I should be able to look at the distance, pace and heart rate and see how things line up.

This chart is matched the best I could without going to far back prior to the half marathon or the coming marathon.  In general it seems like for the same distance and pace my heart rate is the same or lower then last fall.  Where heart rate and pace are the same I'm going further.  This is enough to convince me that last falls time is valid to work from.  Now how does a 2:09 half compare to a marathon.  Is that the equivalent of running a 4:18(2x2:09) full?  Fortunately there's a great tool out there by McMillan Running, the McMillan Running Calculator.  This site has been a tremendous asset to me ever since Rick first showed it to me. By entering in my race time from last fall it will project out what I could run races at other distances at.  In this case my 2:09 half marathon projects out a 4:32 marathon.  After all this science, I'm going to introduce a bit of a fudge factor based largely on intuition and give myself a window of 4:28 to 4:38 for a goal.  This should be what I'm capable of in good conditions.  If conditions are poor, like they were last year I'll need to change my goal but at least I've got a good place to start from.