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Article "The "Ecole Polytechnique", 1794-1850: Differences over Educational Purpose and Teaching Practice" in The American Mathematical Monthly Vol. 112, No. 3 (Mar 2005), available on JSTOR, lists in Table 2 "by years of enrolment the students who later led distinguished careers in and around mathematics at the school and/or elsewhere."
For the year 1805, the only name given in Table 2 is Cauchy.
Whoever it was that scored better than Cauchy on the 1805 entrance, they didn't become notable in Mathematics.