If you do a bit of a search you will find some stuff on sectionals in Just Racing. The site is right into it.

Problems I see with sectionals is they are more likely to be of merit on small US dirt tracks where the sectionals are vital info. for serious handicapping [a bit like the dogs here]. Aust tracks offer up many different times even for the same tracks in same condt. due to minor differences in surface condt. and rail movements etc. You often see records being broken in very average class races, just due to condt. on the day.

I try to take an average from several runs for sectionals and distance times for any runner.