The last time I did a similar workout I managed to rally and hit the paces. The last time I did that workout it also wasn't 85 degrees and a few weeks post marathon :)
The workout got modified a little bit and was 4 sets of 800, 600, 400 (82 seconds recovery, 80 seconds recovery, 2 minutes between sets) Goals were 2:50, 2:04, 80. The 600s were not even close and pretty much after the first set I just had to settle for effort, there just wasn't any more speed to be had in these legs last night! Good workout even if it was slow!