The BB is the best place to start when adjusting timing for optimal performance.
Here are some things which can make the BB NOT optimal:
The octane of the fuel in the tank.
The points gap.
Wear in the timing gears.
Altitude.
Tappet clearance (normal vs heavy duty).
All of these will affect performance, and may require more or less timing to provide for best performance.
I am a fan of adjusting to maximum vacuum, then backing off a smidge.
Carl
Last edited by 52Carl; 04/28/2015 3:04 AM.