I have been a Mortgage Broker for 17 years. In that time I have never seen fixed rates this low. I would stick with a 15 year fixed if you pre pay that much. Very few ARMs have as low a rate and only set you up for a possible problem when they adjust. At that time for many ARMs there is no cap on the adjustment so if rates go crazy you are stuck. If you plan on a short time within the lock period you could be OK but if you change your mind later and stay you are at the mercy of the economy. You can call me at 616-546-6309 for more.