It really depends on the motor, timing, etc... I don't have all that much data for 12 turn motors, so it's hard to say definitvely...
One thing is for sure a 12 turn will put out more power then a 19 turn pretty much across the entire RPM range.
I'll try to give some examples in the next day or so. Right now, I've got to get some other files off of another computer before I can put anyting up on the internt that would be helpfull in this discussion.