The quantity or quality of differences on a molecular level do not necessarily relate the the quantity or quality of differences on a gross physical level. The molecular differences that lead to certain genetic diseases can be very small but the effects can be profound.
Anyone who says that the work hasn't been done, or that the definitive answer is to be found in the shape of skulls rather than in genotype, is trying to sell something and it usually isn't something nice they are trying to sell.
Please note that I'm not simply talking about skull shapes, though I don't think it's unreasonable to wonder whether the shape and size of a brain affects the function of the brain and whether the shape and size of the brain's container (the skull) reflects or determines the shape and size of the brain and thus how it functions. I'm talking about studying the distribution of just about any trait along racial or sexual lines. All such research has become off-limits on the basis that it must inherently be racist or sexist.
And the difference is cultural, not genetic. Middle class black children raised in houses with books do much better than lower class white children raised in houses without books in just about every measure. Family income and literacy are far better indicators of academic success than skin color.
As I said, I believe this, too. And it's my relatively certainty that this is true that makes me not fear such research. Properly done, such research should show that skull shape and brain size really do have no impact on general intelligence.