How does this research deal with the fact that a longer crank offers more leverage, and therefore more torque? So while a rider may not be able to spin a longer crank as fast, he/she doesn't have to because the increased leverage allows them to gear up a bit. This is why it seems to me it comes down more to personal preference.

I remember reading a study a while back that showed shorter cranks offered more performance, and while it's fuzzy in my memory now, it seems it had something to do with the amount of oxygen used by the rider.

If you have links please post.