I dont think that there is an optimal hair length.It?s a case of trial and error (as it is wiv most things in fishing) in finding what length works for the size and style of hook being used. Also bait size needs to be taken into account. No good fishing say a 6inch hair wiv a single peanut on the end of it is there, (no doubt somebodys going to have tried it and caught, Cakey?).If you are missing runs or suspecting the fish are mouthing your baits and not getting hooked, play around/adjust the length of the hair, you may have it too long, fish are picking the bait up but not the hook wiv it, like i said play around, it could make all the difference.