I ran a quick analysis over a 3 month period (Oct-Dec 2001) looking only at gallops with at least a $50000 win pool - this gave a sample size of about 2700 race winners. I compared the 15min price with the final dividend (based on Tabcorp figures) and it gave the following:

44% firmed by at least 10%
25% were steady (less than 10% movement)
31% were drifters by at least 10%