As shown here the output voltage cannot exceed 11V, and the current will not exceed 24mA. By referring to this I can see that the maximum current swing of the op amp in simulation with a 12V source is 11V. Am i correct in saying this is what you mean by getting a feel for it?The reason why you still do not understand the significance of the headroom is because you won't do what I recommended all the way back in the first handful of posts in the original thread. Run a simulation that plots the output characteristic of the opamp so that you can get a feel for how it behaves and what it will and won't do.