1-- No data, just comments from various people. Nothing firm. I did some research and that article because the question had come up, none since. If you want to do some more, be my guest-- just make sure you ask the right questions to the right people.

2-- You do understand that the same people are making both the dirt and grass figures and using the same process, right? So if we are making a mistake with one, we would make it with both-- right?

3-- Most of those drugs you mentioned help horses run faster, in many cases by helping them breath better, in others by reducing pain during a race, and in the case of steroids-- see Marion Jones. There are also other drugs we have discussed here at great length, like alkalizing agents.

4-- By the way, aside from cushion depth, there has been a major change in the sand/clay ratio at many tracks over the years. This was done to help them dry faster, and it is why you don't see the muddy/slow tracks you used to when tracks get wet-- many get faster. The more sand the slower when dry, compared to ones with higher clay content.