On the topic of changing track speeds, here's an interesting presentation by Jerry Brown (Thorograph) from the 2004 Handicappers Expo which essentially states the the speed of racetracks actually change from race to race most of the time because the moisture content of the track only stays consistent if water is added at the same rate that it's evaporating. This is almost impossible as the moisture content is affected by everything from wind, temperature, humidity, sun, track maintanence, how often the water truck comes through etc. Thus, the speed of a fast track with unchanged weather conditions can actually vary quite a bit over the course of an afternoon. It's an interesting presentation for those interested who are figure-oriented.
http://www.thorograph.com/archive/fi...slide_show.ppt