I don't think there is much correlation. This depends on the environment available. For a kid able to get real differentiation, 150+ in a regular classroom might be fine. For a kid with access to a highly gifted program, no skips may be needed. For a kid in a lousy school with no group ready for more advanced work and IQ of 150, many skips might be needed. For a kid in a high-performing school with an average performance well above grade level, grade level may work fine even for a very gifted kid. For a super social kid mostly interested in social dynamics at school, academic level may not matter much compared to social fit.
I think achievement is much more relevant than IQ. If a kid scores 150 IQ but has severe dysgraphia and cannot write 20 pages a week, then taking AP literature at 10 may not be appropriate. If a kid with a 125 IQ loves literature and writes easily, the course might be fine.
