8-10 inches should be plenty I think. I can generate an awful lot of power with a full 10 inch backswing, I can't imagine needing to hit the ball any harder on a non-break shot.
FWIW, check out Earl's bridge length from 1988
http://www.youtube.com/watch?v=vHQw9T5uvyk
Snooker players are generally taught a 10-12 inch bridge. This is one of the best position shots I've seen, makes Corey Deuel's version on the pool table seem very easy. So what the red didn't pass
http://www.youtube.com/watch?v=AIoPHYHaaDg&feature=related
FWIW, check out Earl's bridge length from 1988
http://www.youtube.com/watch?v=vHQw9T5uvyk
Snooker players are generally taught a 10-12 inch bridge. This is one of the best position shots I've seen, makes Corey Deuel's version on the pool table seem very easy. So what the red didn't pass
http://www.youtube.com/watch?v=AIoPHYHaaDg&feature=related