my speedwork mainly consists of 200s at the end of runs. Two mini-workouts I've done a lot in the past are:
4-6x200 at mile/3k pace, 200 jog continuous. certainly some aerobic benefit from averaging 5:45 to 6:00 per mile for a mile or so, or if I'm doing this as a stand-alone workout, up to 4 miles.
6-8x200 at 800/mile pace with a minute or two of standing recovery. Significanly less taxing, but also significantly faster on the 200s because of the complete rest.
Which one is a better stimulus for a 5k through marathon runner?