Sorry if my response is too lengthy. I'm only in Year 8 (at James Ruse Agricultural High), so there's not too much advice I can offer (other than things I've heard from older students).
Can I just say, it doesn't really matter which of these schools your child goes to. Most students are able to obtain the same study resources regardless of which school they go to. However, there is the competitive element where some schools put more pressure on students to do better. If your child thinks they may be doing well in their new school, they probably aren't compared to those in the top schools (sorry, I don't mean offence).
A good indicator of how well a school performs is its "strike rate of distinguished achievers", basically the success rates of its graduating students. To give you a rough benchmark, the best selective school (James Ruse) has a success rate of 77.42% from the latest HSC.
1-Cherrybrook Tech's success rate is 21.1%.
2-Carlingford High's success rate is 18.6%.
3-Chatswood's is 21.3%.
4-Epping Boys High's is only 17.4%.
All four schools are more or less equal in standard. The marginal difference in success rates is negligible.
The main point here is which school your child will find to be most helpful. I'd recommend Carlingford High, because it is very close to James Ruse (the top school) and students often meet up at tutoring centres to discuss homework and study. It would be good if your child could find some friends in the top selective schools; that's usually the way to compensate for attending a poorly-performing selective school.
Additionally, Carlingford (the suburb) has a high Asian population, so your child might fit in better. I think Cherrybrook also has a large Asian population (though not nearly as large as compared to Carlingford). Don't take my advice too seriously, because your child may want to attend one of the other schools. Students are usually able to switch schools during high school, so if your child doesn't like one school, he/she may be able to enter another (by way of examination or application). If he/she enters by application, he/she will need a good record of extracurricular activities and have a good academic performance.
In regard to your second question, most schools do have similar subjects. This is because they are based on the NSW curriculum. However, schools have different priorities, e.g. Sydney Boys High School is very sports-oriented and James Ruse is very maths-/science-oriented. If your child has a particular strength, he/she may choose to attend a school that leans towards their strength.
Some schools may lack elective subjects that they consider to be useless, e.g. James Ruse drops compulsory music after Yr 8, but continues compulsory Agriculture until Yr 10. (Music is still available as an elective subject after Yr 8, though.) Do some research on this forum and ask other students what their schools have for core/elective subjects, I can't say much about those four particular schools you're asking about.
Once again, I apologise if this answer was too lengthy.
