Go and look at the schools. My child was at Chesterton for a short time, but I removed him from there due to some personal care and security issues. I also found the admin staff incredibly hard work.
Now at John Burns I am a lot happier, but the head is very difficult to talk to (if you are trying to get them to do something/change something, just forget it).
The main differences between these two schools are: Chesterton is a two form entry school, and John Burns is a single form entry school - so there are effectively twice as many kids at Chesterton as John Burns. John Burns has a lot more room around it in terms of play space - without even taking into account the number of pupils. Chesterton is also right next to a main road (so if there really is a negative effect on health/intellect from traffic particulates…), where John Burns is quite a way from major roads (probably about as far as you can get in Battersea).
I do not know much about Wix, I think the French aspect is good (but Shaftesbury Park also has a bi-lingual class intake - but *very* small playground). One of my neighbours has her older son at Wix, but her younger one at John Burns - not sure why she made that decision.
John Burns has many after school clubs, and volunteer input from Kids Co, the children seem generally polite and well behaved, I don't hear stories about consistent behaviour problems. They had very good year six results recently - but for some reason this seems to be on a smaller sample than the whole of that year (something I haven't enquired about, but does seem odd to me).