I see your point about lower number being a speed collapse. What I would argue, particularly in routes, is that the 6f early pace is a better indicator of what a closer's chances are. I haven't seen it approached quite the way I think you are looking at it, though I'm intrigued. I like what you say about efficiently rationing speed, and I believe that's a particularly useful number when looking at younger horses or horses exiting races with multiple speed demons.
Faster late pace is a function of slow early in most cases. Certainly makes it more difficult to close into, but I'm of the opinion that late pace is tough to interpret without knowing the early pace.
When you're using the other races to create a variant, you have to see how the other races were run. If there are 4 speed duels where the pace collapses, the late variant will be high, but a race run differently with a slow-early speed on an open lead would throw that race out of whack.
Now I'm confusing myself
. I know what I'm thinking, so I hope I'm communicating it.