There are very few things that are predictive of what MCAT score an individual will get.
I think the only things that are actually linked might be the verbal score of the SAT at the VR of the MCAT. The SAT Math might be linked a little bit, but I don't think it was significant.
Other than that, in general, better GPA's do better on the MCAT, but I don't think the R value is very high on that...