Worker, I wouldn't be surprised if Speer's BC wasn't a little overstated, but I don't know what it should be, especially when you put it next to the Berger. .006 really is "nothing", and there should be "something".
DR, the bullet composition is related to "sectional density", which you actually indicate in your discussion when you reference "mass for volume (density) and cross sectional. Ballistic coefficient is solely related to shape, and the manner in which a bullet encounters drag.
While heavier bullets often have higher BCs, it is more because they are long for caliber rather than the fact that they are heavy. Many high BC bullets will have a large air pocket in front of the lead core.