alt Hacker NewsDid a Google search, and the only actual, definitive thing I found was this:
https://pmc.ncbi.nlm.nih.gov/articles/PMC5008436/#tbl1
Note that it's an IQ of 128 vs 125 for humanities. With the small sample size, it's basically noise. And given that this is Oxford, I would expect the average PhD student to have less than these numbers.
Oh, hold on, I may have gotten my numbers mixed up slightly. 145 might actually be for working, full time pure mathematicians - sorry about that, I'm double checking now.
EDIT: My massive bad, it looks like I accidentally bumped everything up a standard deviation in my head somewhere. Jesus. I should update the numbers in the original post. Maybe I should also consider getting a math PhD after all, apparently I'd be ahead of the pack in that case.