I agree with Neal and Michael 100%. One must consider the physics of leverage.
I'll add that the practical limits will vary by individual. You need to take into consideration how you like to clench because it will impact your choices of pipe length, weight, and button size. I now vary my clenching style based upon the pipe.
Big, full bents need a comfortable button to work. If you clench transversely, with the button held firmly between your premolars, you'll be able to manage a longer, heavier pipe than clenching perpendicularly, with the button fully behind your premolars. So, your clenching style may dictate the shape of the stem and button, or vice versa.