SAT score for New Rochelle vs everywhere else in NYC (quite a bit more unbiased since it is a national test):
SAT Scores
It is comparable to the good NYC public high schools, like Bayside/Cardozo in Queens, in other word barely acceptable.
However, it is nowhere near the specialized high schools. Even Scarsdale would only be comparable to a low end specialized high school like Brooklyn Tech, Stuyvesant is easily a full tier higher (1405 vs 1256 from Scarsdale). That is the beauty of NYC, if you are exceptional, you will get an opportunity to attend an elite school as good as any suburban public schools (and better than 99% of the private schools that don't even dare to publish their SAT scores).
I got into Brooklyn Tech myself two years after I came to the U.S., never spoke a word of English before I got here, it wasn't that hard. In my opinion you are robbing your own child's potential if you go with New Rochelle over an NYC school. In NYC they at least have a chance to get into an elite school, in New Rochelle they are doomed with mediocrity.
I would only consider a Westchester school if it is one of the top tier ones like Scarsdale or Rye. Paying so much real estate tax for a 1000-1050 SAT score school is retarded. I rather have my child grow up in say, Forest Hills queens (964 SAT score, only half a tier lower than low end NR schools), and let him/her take the SSAT and see what happens.