. . . the first issue [Are persons of color, specifically african Americans, possessed of lower intelligence ?] is purely empirical in the truest sense of scientific method.
Purely imperical? Yes and no.
Sure, the question is testable by carefully designing scientific experiments and surveys, recording the data, and then examining the results. But there is a crucial principle within the scientific process that mandates you control or account for every significant variable.
In the "hard" sciences, like physics, this tends to be much easier because there are usually far fewer variables involved and the basic principles are often defined by established laws that are precisely quantified (like the law of gravity or Ohms law)
Studying human behavior and attempting to form justifiable conclusions about how or why people act the way they do is vastly more complex and includes so many variables that it becomes virtually impossible to design experiments that adequately control or account for them all.
In this particular example, if you're studying human intelligence and want to find out if there are inherent (genetic) differences between two different races, then the difficulties quickly become apparent.
1) "Race" is a social construct, not a biological one. There is currently only one human species on Earth so it can't be defined that way. Traditionally, when these studies were first done, skin color was the determining factor, with dark brown skin making one "Negroid", yellow skin making one "Mongoloid", and light tan skin making one "Caucasoid".
That classification system has long been discredited as grossly oversimplistic and arbitrary. Subsequent attempts to define "race" in a valid, quantifiable manner have all met with failure because the migration of humans across the planet over the last few thousand years, and especially the last few hundred, has mixed our genetic lines into an indecipherable conglomeration of various traits.
2) Nature versus nurture. Probably the most difficult task in studying human behavior is determining the relative cause and effect of genetics versus environment. Many volumes have been written on this topic and I couldn't possibly do the subject justice here, but just understand that virtually every experiment on complex human behavior will always be severely compromised by the near impossibility of adequately controlling all the variables involved enough to provide untainted data to study.
3) Intelligence. Early efforts at defining intelligence were so narrowly focused on what the experimentors considered to be most important that they were little more than self serving tools to declare their own ethnic group the smartest people around. It is now widely accepted that one (or a few) simple metrics is entirely inadequate to describe all the factors that make up human intelligence.
Furthermore, intelligence is not the hard wired genetic constant as previously thought. Nutrition abd diet (especially during childhood) plays a large role in the ability to learn and think creatively. In places where nutrient rich food is abundant and readily available, brains can achieve their full potential for intelligence. Live where nutrition is poor and hunger is common and the body steals resources from the brain for survival and that leaves intelligence as a low priority.