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Stiffness, weight?
More money (or just better judgement) can certainly get you more of one and less of the other, but that doesn't answer the question.
Or if you're gonna be spendy, go the whole hog
At the margin, all builds are compromised by budget constraints. If that bike is meant to go fast, it's still in need of better wheels before any change to the cranks is going to be a better performance buy.
What performance benefit do you think accrues to spending more than that on cranks?