i used to keep stats on this..... not all races, just the ones my system bet on. I did this to see if i could improve it by removing any stat that was negative. i no longer have the stats as i made judgement years ago on my findings.

1st up strike rate was much better then 2nd up with 3rd up the most succesful.
Also interesting horses having their 5th+ start after a spell was only average

Part of my conclusion was that the market knows how horses handle each outing. i.e. a good first up horse was shown in the market where as a horse needing the run was larger odds. Now thats might sound obvious but horses rarely turn their precedented stats around in this area. I check every horse for this particualr stat, every race......it rarely lets you down as a guide.