xmas. May Marathon?

So it's Christmas and I will go for a run later on. Think 5 miles, with some speedwork in there. Ran at lunch on Tuesday, just over 5 miles. Yes - it was chilly, but still in shorts. Did wear a 2nd short sleeve shirt under my l/s one. It was about 35° but mostly sunny. When it's that cold, I have started running with a head wrap that just covers my ears. Works great!
Am now thinking of a marathon late May/early June. I know I'd have to travel for that (none around here that I know of due to warm temps, which I do not like running in), and I may be traveling to Ohio over Memorial Day weekend, so I may not want to travel back to back like that. We'll see. Too bad the Cleveland Marathon is the weekend before I will be there! I will do Richmond in the fall, running with my brother. I figure I would not be able to run all out in that one because I'd want to run it with him (he may be faster than me - but still), so I was thinking I could do one before that and push myself some, what I did not do in NY. I will keep looking...
Oh - also trying to figure out if I should try my older shoes out again. When I had run in them - I would get some pain in my right shin area. I never knew if it was because of my training or the shoes. I am in Asics 2130's now ("structured cushioning") and I have 2 pair of Landreth's and one pair of Nimbus (both "cushioning"). ANyone know if that could pose a problem? I'll ask over at Fleet Feet next time I am there...