But do you think that the tugging increases speed, or that fast, highly driven dogs are just more prone to enjoy tugging in the first place?

I have shelties, mine have all started out liking to tug, especially the last two; but the longer we go the less interest they have in tugging and the more they have in running the course itself. They will do a perfunctory tug “if I must” before we run. I think it is a multi-factored problem, they are very high drive and LOVE agility itself; despite being very food driven I also have trouble getting them to take time for food rewards on the course (with my younge dog since we started running longer sequences I try to reward on the contacts and he just lets the food dribble out of his mouth, all he wants to do is GO!). This can be problematic. Also I find that despite having intact, high drive males, they are pretty submissive and want no part of any altercations with other dogs; they tend to be reluctant to tug at trials with other dogs around, at least before we run- coming off the course when they are revved up they are much more willing to tug, often quite vigorously. They like to chase toys and have reliable formal retrieves, but seems like consistently the older they get the more they’d prefer to chase the thrown toy (or another dog retrieving the toy) till it stops moving and then come back without it.

I suppose both of these things are holes in my training program . I do use toys in training but I have only in one instance had that toy that my dog was INSANE for (that was Andy’s squeaky rabbit fur mice, and he only got them for seconds at a time while doing obedience).

I would love to have seen the whole video as well .