I recently purchased the 100 mile plan and have dropped it into my calendar to begin 12/18. I've noticed that it's all HR zones for the training runs and I don't see any speed zones. I also noticed that the performance test is different from The Cool Impossible. The book has us do a 1 mile test and a 20 minute test to set HR and speed zones.
Is there a particular reason/theory to not use the speed zones in the 100 mile plan? I found that the set HR/Speed zone runs in The Cool Impossible were not only fun but where I improved the most.