I would be cautious about putting too much weight on GPAs as there is so much variation from school to school (which is why SAs tend to recalculate). Even with a recalculated GPA, the SAs will need to look at class rank, academic environment, strength of schedule, etc. when evaluating a candidate's GPA.
From the USNA Admissions FAQ... Q: "What Grade Point Average do I need to get an appointment?" A: "There is no specific GPA minimum. However, you should strive to be at least in the top 20 percent of your high school class."