The studies quoted above, that appear to support overspeed, in fact do not. The distance tested was 35m. Even for slower athletes, this is almost all acceleration phase. The uphill portion of the training alone could explain the improvement. To test for the contribution of the downhill phase, there should have been a group that did uphill and horizontal, to be compared to the uphill and downhill. A downhill and horizontal group would have been nice to determine if the downhill training actually improved upon horizontal only training even in the absence of uphill training. Unfortunately, these groups were not tested, so it is impossible to seperate out the improvements resulting from the uphill training from those that MIGHT have been derived from the downhill training.
Having said that, I do like contrast training and also think that overspeed accleration to Max V immediately transitioning into a flat flying 20m or so, has benefits. Charlie actually supported this notion from a poster in this group who discussed using the sloped bank of an indoor track to rapidly acclerate to Max V before running on the flat for an acclerated flying 20m or so.