Wikipedia says that people with autism and asperger's outperform other people on Raven's tests. Most people view ASD individuals as seriously cognitively impaired and they are often seen as low IQ, so I have trouble with your assertion. It suggests that people the world sees as highly impaired whose lives typically are harder than average are smarter than the rest of us. This completely flies in the face of every definition I have ever seen for IQ as a general predictor of competence.

Wikipedia also says the answers for Raven's matrices have been leaked, making them useless as an assessment tool.