I haven't looked for any recent research in this area but when I saw some way back when it was, in one sense, somewhat depressing. I forget if it was for undergrad or MBA programs but, as I recall, the correlations were basically to SATs/GMATs and class rank/grades. Of course, your results will vary depending on how you define success but basically quantitative hard measures had the most predictive value.
This was a long time ago and I don't remember the details. One commonly-used quantitative workplace success metric is compensation/salary, which is not necessarily unreasonable for MBA programs but can be more problematic in other areas.
And you're right. It's not really surprising that getting good grades/test scores at one level of school correlates reasonably well with the same thing at another level. Which I imagine is one reason universities/grad programs generally don't optimize purely on that metric because their objective isn't solely about cranking out students who study well in school.
ADDED: This, by the way, is more or less just a variant of general intelligence measures being correlated to a lot of outcomes. The SAT and so forth aren't intelligence tests, but I'm sure they're very correlated.
