Hi again, rktb, just got back to this! It's rather strange being able to ramble at such length, since it's not something I generally discuss with other people, since everybody has their own axe to grind.
I think what you say about your dd being turned off learning and enthusiasm would ring major alarm bells for me. My dd1 was turned off school, but happy to learn and do things at home, almost despite the school. But she is more focussed than most children, even when she was quite small. My ds is doing okayish because he's in quite an able and well-behaved class (Y2) with pleasant (if slightly ditsy) teachers. He's quite compliant, a bit of a pleaser and keen to try hard whatever the circs. So although I'm sure he could be doing better in a more focussed environment I'm not going to worry about it yet.
Do you have plans for secondary yet? That might affect the decisions you make now. My dd1 has got a place for September at one of the north London (state) grammar schools, which I'm sure will suit her down to the ground. Not sure about ds yet -- there are various good Catholic options, but might go private for him. Don't think the state selective options would work for him, cos he's bright but not superacademic.
If you went to eg. Children's House you could move at 7, but their school is still a bit of an unknown quantity. City of London girls have an intake at 7 (dd1 was offered a place there for Y3) but it is quite a high-powered machine of a school, possibly not for more sensitive or unconventional souls, which is why we didn't go with it. Statewise your options are limited at 11, though Mossbourne is worth keeping an eye on. You'd have to move, though, their catchment is quite tight. From what you've said I can't see the urban gritty vibe of Stoke Newington School appealing to you?
Our children must be quite similar ages, since dd2 is 2.5 as well. But we're looking at nursery class starting 2007 -- I thought Cavendish only take them from 3+? When do you have to let Cavendish have your decision?
As the other poster says, I don't think the Catholic element would be a problem for you unless you are massively anti-religion full stop. I got the distinct impression that Cavendish are trying to be all things to all people: when I went round there was another couple visiting who clearly weren't Catholic, while I clearly was (from the questions we were asking) and it was mildly entertaining to see the head trying simultaneously to make it sound as if the school was Catholic enough for my requirements while not overplaying it for the other two! The RE is clearly multi-faith in nature (they'd had a Muslim parent in to talk about the Haj just before I visited), so as long as you can cope with a statue of Our Lady in the prayer garden and a bit of God-talk coming home you should be okay. FWIW if I were a non-Catholic I wouldn't send my child to most Catholic state primaries, nor to eg. St Mary's Hampstead or the school we've chosen for dd2, but I wouldn't have the same reservations about Cavendish.
If you're still concerned, why don't you phone the head and ask if there are any non-Catholic parents who might be prepared to share their experience with you? You could ask how many pupils are local to N1/N16 while you're at it. You do see the uniform around Upper Street quite a bit, so there must be a few. Otherwise they can also make local friends through out of school activities, eg. ballet, brownies etc.
Maybe we should meet up for a cup of coffee in the Blue Legume, so we can obsess in greater comfort and without the RSI!