I think Guest Russ hit the nail on the head! "Sounds fine" is the criteria I use when adjusting my banjo head (which is very rarely indeed). Although it is now a Remo, I also used the same criterion when I had natural skin banjos.
If I purchase a torque wrench, I will need to also purchase a humungous case (instead of the neat little gigbag I currently use) to accomodate the banjo, torque wrench and (inevitably) anorak I will have to carry! (;>)