Notes
(1200, 1000, 800, 600) x2 @ 5k pace. 1.75 mile warm up in light snow with strong winds. Tripped in a pothole in the sidewalk, but seemed to have recovered OK. Had a small amount of pain (more of an ache) in the food at the end of the interval workout, but I don't think there's anything lasting.
So, 5K pace for a 4:20 marathon is 64 seconds per lap. Pretty much hit it every time. Did 6 laps followed by 3 minutes rest, 5 laps with 2.5 minutes rest, 4 laps with 1.5 minutes rest, and then 3 laps. Repeat after a 5 minute rest.