We have DDs at Holy Cross, in both the infant and the junior sections.
Overall we are very happy with the school. The pastoral care is fabulous. Our DDs are quite different characters, but both a very happy there and love their teachers, their friends, everything. The teaching is good, and the newer teachers in the infants are very very good with some really innovative ideas. That's not to say the older teachers aren't good, my older DDs current teacher is a long standing staff member and I think she is fabulous.
It's not perfect and no school is. There will be things that annoy you. The school is very hot on it's rules and keeping them. They are also very upfront about running it that way so you know that when you sign up. But as a parent I have on occasion felt like a naughty child...! I know some parents feel the sports provision could be better, especially for infants. And the school could be better at providing information for working parents.
The year 5 and 6 girls you meet come across as very happy, well rounded and confident people. And I can see my older DD (who is in the juniors) developing into that sort of person, having been there a number of years now. She is articulate, thoughtful, and is being given many opportunities to stretch her wings.
On areas - girls do come from Wimbledon, there are a some in each of my DDs classes. A lot obviously from Kingston, New Malden, Raynes Park. Some more towards Richmond, and a few outliers from much further afield. I would suggest you try the school run in the traffic one morning if it's a concern for you - the traffic along Coombe Lane and over the A3 can be horrid.
Good luck with your decision!