How about this: see what February brings. It sounds like you might be into the running and are committed to doing the marathon -- completing a marathon is an exhilarating feeling and accomplishment, although, you might be hurtin' a tad when you cross the line. I remember when I did my first marathon (Boston in 1983)...trained through the late Fall and winter (although, a just a bit colder and snowier in Boston than in Austin -- I lived near Heartbreak Hill and trained on it quite a bit) and did just fine...although I was tired and sore after the race, I recovered fine and kept on running...of course, I was a bit of a younger lad then...be diligent and step up your mileage carefully and you will be ok (all else being equal)...completing a marathon is more accessible/doable than most people realize...go for it, then, see where you are for cycling and take it from there...plus, I thought racing started up in March, not February...I recall that the Driveway started in mid March for 2008...good luck