Yesterday I did the aging veteran's version of speedwork: 8 X 400 with a 200 jog rest. I don't remember the last time I did 400's (I'd guess it was spring or summer of 2000 - I could look it up - probably will - well, wait a minute, I'll check my log - never mind).
Nonetheless it was a pretty good workout, although I had considerable energy left in the tank afterward. My goal was to run 1:45 (7 minute or roughly 5K pace - although I really had no idea where I was fitness-wise).
Time to push it!