Notes
My first interval workout in 11 months or so, I decided to start out the progression with 5x600m at 3k pace. I don't have a current race over 3k to extrapolate from, so I just chose a 17:30 5k and went with that. The first interval was a pace experiment, then the next two were on rolling terrain and I was able to hit my goal pace. The 4th interval was about 400 meters of gradual uphill, and my pace suffered pretty badly there.
Overall I would say that I probably was a little ambitious with the pace, and I probably would have had a harder time with it if my recoveries were less, but I wanted to keep the recoveries around 2 minutes so that I didn't overwork myself too early in my interval season.