I ran 5:47, 4:49, 4:40, 4:24. During the same period I cut my 5k from 23:00 to 15:27. Not earth shattering but neither is my talent. Just the same it was a big drop from when I started and was getting last place, literally. What did it? Miles. Frequent 2 a days and now and then 3 (morning, noon, night). 5:00 -> 14:55 seems quite reasonable.