I would wait to look at your Physics GRE before making a recommendation with respect to where you should apply. Your research experience will definitely help you, in particular if you publish your results and your professor is known in the US. He should emphasize that, and maybe he can give you a competitive edge at Stanford. I think that the best thing you can do is to apply to a wide spectrum of universities... a few top 20... more top 50... maybe some top 100
just in case. You have a chance if you do well in your physics GRE.
P.S. Is not as trivial to convert grades with 10 as its basis to 4, is not just a simple ratio. You have to assign 4 points for each A (above 90), 3 points for each B (above 80), 2 points for each C (above 70), and 1 point for each D (above 60). You then multiply your "grade" times the number of credit-hours of the course. Then you divide by the total number of credit-hours. Most probably, 6.4/10 is not equal to 2.6/4.