It is, to put it mildly, not at all well established how SES and assessed intelligence interact.
Likewise while you can look at historical Jews as a poor population with high IQ, you have the confounder that even then Jews placed a strong cultural value on education and intelligence. And therefore, even while they were poor, Jews were likely to work to improve themselves on both. Therefore this leaves open the question of how much of the difference is due to this cultural factor versus innate genetics.
In the case of Vietnamese boat people, we have families that literally risked their lives for a chance at a better future. This attitude taken to a new country suggests that we should expect them to make the most of any opportunity that they can find. How much of their subsequent success is due to this attitude?
On Nigerian immigrants, I'd need to see a source to believe your "generally better social outcomes" comment. https://en.wikipedia.org/wiki/Nigerian_Americans puts the 2018 median household income for members of the Nigerian diaspora into the USA at $68,658. https://www.census.gov/library/publications/2019/demo/p60-26... the median household income for white non-Hispanic households at $70,642. At least on the easiest to check social outcome, whites are still doing better.
That said, Nigerians who arrive here tend to be motivated and well-educated. I'm not sure how you can distinguish that from genetics. Doubly so since the poster child for racist claims about IQ is the poor performance of US blacks. Blacks whose African ancestry includes a significant share of Nigerian.
So yes, we can cite volumes of statistics. And it is easy for find lots of books like The Bell Curve that actually do. But when you dig in you won't find a single statistic whose difference can be clearly attributed to genetics rather than some cultural factor.
I think it is more likely that culture drives genetics. If you have a group whose culture favors intermarriage, where marriage is encouraged and even arranged between families with intellectual success, and which enables the resulting couples to have many children, that would tend to drive the genetics of the group.
Sexual selection is tied to culture.
For example from the middle ages to the present, individual self-control greatly increased and this caused homicide rates to drop by a factor of 10. See https://www.vrc.crim.cam.ac.uk/system/files/documents/manuel... for verification.
Elizabethan England was incredibly bawdy by all accounts. And yet the same country a few centuries later was Victorian England, one of the most sexually uptight societies on record. Genetics didn't change that much, how did that happen?
Germany from the mid-1800s through WW 2 was one of the most warlike societies imaginable. Germany since has turned into a country of peaceniks with no interest in invading anyone, and who are unable to even cough up what they promised for self-defense. How did that happen?
The truth is that while factors from genetics to parasites like toxoplasma can impact culture, culture changes far too rapidly to be dismissed as simply an outcome of genetics.
This is an isolated demand for proof. At the level of proof you're demanding, basically nothing can be said about anything in terms of social science one way or the other. There are basically never 'single statistics' that are isolated from all alternative explanation.
Instead, one should apply the same standards and skepticism to all hypotheses. In this case, both for and against genetic/cultural explanations.
(Even so, "you won't find a single statistic whose difference can be clearly attributed to genetics rather than some cultural factor" is untrue; differences in athletic performance satisfy this demand.)
I'm sorry but this is blatantly false. "Innately better" is a vague and inflammatory term, but if you define the measure, we can use straightforward statistical techniques to find correlations.
Simple example: East Africans outperform others in long-distance running. In sprinting, west Africans outperform.
We can separate confounders out because we have large data sets. You don't have to just try to compare populations as a mass. We can, for example, look at performance only of black people raised in white families. Or rich black people. Or white people raised in black families. Etc.
Taking the example of IQ, which is the most important statistical measure in these discussions, we can also look at poor populations with high IQ, like Jews (at certain historical times) or various groups of people from East Asia. Vietnamese boat people are a great comparison. It has to be explained how they were so successful despite facing the very similar or arguably worse challenges (e.g. holocaust) as other population groups.
Or look at subgroups of black people, like Nigerian immigrants to America, who have generally better social outcomes than average whites.
All this has been studied to death for decades and many conclusions are well-supported by statistics (at least as well-supported as lots of noncontroversial findings).