Are you plugged into an Isliington gossip network, Spacemonkey? If you are, I may be telling you things you know already, but here goes.
The ones you mention are all popular schools with a middle class contingent. I know people with children at all except Thornhill. Tyndale have had some disruption with headteacher turnover, they have a pretty mixed intake and the usual complaints about inner-city primary schools, but not catastrophically so. They do lots of arty stuff and music lessons too, apparently.
Hanover had a big hiatus a couple of years ago when the headteacher was sacked for fiddling the sats. Rumour has it she was also fiddling the intake in favour of middle-class kids -- certainly I know kids from quite far afield who have got in. My dd1 has been offered waiting list places there a couple of times, although we're well out of their area. Don't know how the new headteacher has bedded down, but there doesn't seem to have been an exodus.
Canonbury is BIG, but seems to be very successful and again lots of cheerful bouncy kids. I see lots of Canonbury parents at swimming, and there are the usual grumbles, but again no exodus.
I also know people with kids at Rotherfield -- in fact come to think of it, I know one of the governors. They certainly have at least their fair share of problem families, and perhaps less of the arty middle-class journalist/designer contingent than the others, but those people who've stuck with it have been perfectly happy.
If you want more specifics, let me know and I can try to find out.