Of course there is some correlation between the two skillsets (with respect to ability): people who can abstract well can also understand the underlying ideas that are useful for fast calculation, and for both one needs to have a reasonably good memory (to rely on in an exam and when developing a mathematical intuition, respectively). But to be the best in high school 'math' (calculation) requires a degree of extrinsically-driven, dull discipline. One can probably be best in class without taking this degree to the extreme, but among the best in class, many excel at exactly this (and not at abstract thinking), which I find a bit troubling.