In most equine forums you can start a pretty good "fist fight" over bits. Mostly the combatants are working from myth, legend, breed tradition, etc. Few work on fact.
So I was pleasantly surprised when I found the work of Dr. Hilary Clayton, from MSU in Lancing. Here is a short article about some of her work:
Dr. Hilary Clayton Offers Many Prescriptions For Bits
She also has a book on equine biomechanics that I'm trying to get through our inter-library loan system. Failing in that, I'm going see if the UT Vet. School has it and if I can "big deal" a loan. If it's good, I'll buy it (for $60USD).
Maybe I'll just tell Santa to leave one.