To your specific question, my kid had an unweighted 4.0 freshman year. His school did not report numerical percentages, and freshmen could not take AP classes. The valedictorian (Brown) and salutatorian (MIT) also had straight As freshman year assumedly since they both finished with the maximum achievable GPA, or so they announced at graduation (I have no idea how they picked which was valedictorian). I would be willing to bet that most kids who get into highly selective schools have perfect or really close to perfect gpas as freshmen under whichever standard the particular school uses.
As far as pure academic stats, my uneducated guess is that standardized test scores and taking the most difficult curriculum available matter more than minute differences in gpa. At least in my kid’s school, all of the kids in the last couple years who got into highly selective schools were IB kids, while at least some kids with higher or equivalent gpas taking AP classes have been less successful in chasing “those” schools.