Started writing this reply earlier this afternoon, before I had a chance to see the other responses. Just going to post it as is, but apologies for being a bit behind the conversation...
Fascinating stuff. Just wanted to pick up on this part of what Smoove said: "The guy was going to have to race at 5:15-5:18 pace, and was going to do a ton of work at 5:00 pace; so I felt he needed some work at closer to 4:50 pace to make those other paces manageable."
What Smoove is saying makes a lot of sense, and it sounds like the approach he's taken has been effective for the athlete in question. I wonder, though, if there's a distinction to be drawn between doing workouts that are "two steps up" from race pace in order to promote mechanical development and doing workouts that are "two steps up" to promote metabolic development?
This is one of the things that I find intriguing about Canova's approach (from what I understand of it, and I certainly don't claim to be an expert). Canova has his athletes do a very high volume of work just a little bit slower than race pace (about 95%, so for Smoove's athlete about 5:30), particularly in the form of the "long fast" runs. He has them do a lot of work at race pace, particularly in the form of high volume interval workouts. He has them do some work just a little bit faster than race pace (about 105%, so for Smoove's athlete 5:00), but this work is really only a little bit faster and the volume is fairly limited. His athletes do a little work faster than that, but the volume is pretty minimal and the primary emphasis appears to be neuromuscular recruitment and mechanical efficiency.
So, in a sense, it's like the key Daniels paces are shifted one step slower, in the interest of significantly increasing the volume of "specific" training. In that sense, the relative emphasis shifts more to the endurance side of things, though Canova would probably say that he's emphasizing specific speed endurance.
Just to be clear, I am far from being an expert on either Daniels or Canova, and I'm not trying to suggest that one way is right and the other way is wrong. But I do find the apparent contrast intriguing (and as someone with exactly three fast-twitch muscle fibers named Moe, Larry, and Curly, I confess that I find an endurance-side approach personally appealing).