This is a long-winded and strange justification to try and deny the relevance or practicality of IQ. You're worried about coming off as a "heartless asshole" yet concede most people, if honest, "would admit they believe blacks to be less intelligent?" By contrast, relying on a scientific measure and pointing out group differences is simply a statement of fact.

I think.. our evolutionary paths diverged and were substantially different.. and that our brains are significantly different as a result

OK - but how do you prove that African and Euro brains are "significantly different?" If we only we had some kind of objective measurement for intelligence that could show this..

but the difference is probably small

but we just demonstrated in this post what evidence we have indicates the difference is not all that small

that suggested pre civilization humans in cold climates were likely significantly more intelligent than modern humans

This is the "Cold Winters" theory put forth by a number of authors, including Lynn in Race Differences, which is linked in the body. Cold winters theory alone is inadequate in explaining the lower IQ (but larger brains) of Arctic Peoples (~90) compared to Europeans and East Asians - which probably indicates agriculture is a significant part of the equation. But no one knows for sure, specialization could play a role. Humans are constantly evolving even up to the present. People alive today might not be able to survive and reproduce in prehistory or ancient times, and vice versa