I would be interested to see the results for a comparison of black and white individuals with comparable upbringings.

I have a very, very hard time believing this.

Yes, if you compare the cognitive ability of someone in a 3rd world country to that of someone in a first world country, or someone who grew up in poverty to someone who grew up comfortably, I would be unsurprised to see a difference.

I would be intrigued to be linked to any peer-reviewed study that is not colored by those factors.