Researchers have philosophized about and demonstrated that there is a specific kind of knowledge that teachers need that is likely different from just knowing the content itself.
So, there is data that demonstrates that knowledge of content alone is not what good teachers need. Rather, they need knowledge of things like how students make sense of the content, how to design tasks that align with knowledge of how students think and move their thinking forward, how to create representations that help students see mathematical relationships, that sort of thing. This knowledge aligns with what John Dewey called "psychologizing the curriculum," to connect the logic of the discipline with how the learner thinks and experiences the world.
I think that the common assumption is that subject matter knowledge is enough to be an effective teacher -- experts in the discipline could explain what they know and then students will learn it. A faulty aspect of this assumption is the idea that teaching is more than transmitting knowledge. Teaching involves translating knowledge in ways that make sense to the student and giving students an experience to make sense of the knowledge.
So, I don't know of research that correlates between knowledge of the discipline and ability to teach. I just knew of research that shows that it's more than knowledge of the discipline that matters, but instead an additional, more specialized knowledge for teaching that matters.
(I recognize that the research I am sharing is about teaching at the K-12 level, but I think the general principle -- that knowledge needed to teach well is more than content knowledge located in the discipline -- carries over and transfers into the university level.)