My commuting pace depends on a number of factors -- the weather (primarily wind), how tired my legs are, and my weekend riding plans. Most days, I commute at what I would call "tempo" pace -- that is, just my normal speed and not trying to go particularly fast or slow. If I had a hard ride the day or weekend before, I ride at a slower recovery pace. If my legs are feeling good, the winds aren't howling and I don't have a long or difficult weekend ride in the near future, I often push the pace and go as fast as I can. Sometimes I ride fast in the morning and slower in the afternoon, or vice versa. So, in short, the answer is "it depends."