Congratulations that your kid is really smart! I'll choose York, because:
1) The kid is studying happily in York
2) Believe it's not easy to go to "尖子班" and the school supposed to put extra efforts to train up these students
3) KM AM is main stream, internation stream(English-Putonghua) is in PM. I guess York AM provide better English environment over KM AM.
4) I have some friends with the kids graduated from York. The first one is a girl, she is now studying in Good Hope. The second and thrid ones are boys who just graduated this year. One studying in St. Frances, the other studying in St. Joseph. For me, these primary schools are pretty good.