Have namechanged to give my feedback. We have DCs at the Perse. Like every school, there are pros and cons and it's all about finding the right school for your particular child. One parent/s /child/s experience will not necessarily be the same as another's.
In our experience, it's rather like a co-ed grammar school and would certainly best suit bright, emotionally robust children. We don't get the impression that it's standards are 'sliding' and this doesn't seem to be the case, given the very good academic results that are still coming out.
There are loads, absolutely, loads of extracurricular clubs, especially music and sports but lots and lots of variety to cater for all different kinds of interest. Suggestions for clubs from children are often taken up by the school and accommodated.
The only children we know of who do individual music outside, rather than inside school, are largely those who also do it within the school but are now at such a high standard that they need even greater expert tuition outside as well (think diploma level at age 10/11 already). We know a few children who don't do individual music lessons at school because they prefer not to miss a lesson during the school day or they're doing music without wanting to take exams in their instrument.
Our DCs do so many extracurricular activities that they've started to cut down on them now, because of increasing homework demands but you could easily fill every single lunchtime and after school period with a club, plus some early mornings, before school starts.
There seems to be a range of ability from very bright to genius/child prodigy level and those who thrive most, appear to be children with a leaning towards Maths and Science (and music) rather than the Arts/Literature etc. I would say that the 'stereotypical' student is a whizz kid mathematician, a bit geeky, possibly also very musical, maybe talented also at a sport (or not at all sporty). Still in transition from single sex to co-ed., I think the school is OK for girls who can hold their own in a largely male dominated environment and love the science/maths part of the curriculum.
I agree that you need to be the sort of child who can be independent, self-organised and fairly robust, to thrive at the school but I also know of several children not like this that have been supported by the school and are progressing towards these helpful life skills.
I think the school is expanding too much, too quickly and the numbers of pupils per year group and per class (about 26 per class and 5 to 7 classes per year group, depending on what part of the school you're in), means that it's much harder for individual children to be helped, if in need. However, the school tries to overcome this by having a tutor system of 12 children to one tutor, who know them well, although the tutor changes every 2 to 3 yrs.
Our DCs are about average/lower average for their cohorts - so not at all the genius/brightest level - just basically competent/bright enough. This means that for them, some things are harder than if they could cruise along, naturally brilliant at everything and outstanding also, in a particular area.
We think our DCs unlikely to get 13 As at iGCSE level, as many of their peers will - some do the exams a year or two early as well - but we'd hope our DCs would get around 9 or 10 A grades at iGCSE, with the odd B or A amongst those. They're not yet at that stage so we won't know the outcome for a while and can only guess/predict. But this would mean our DCs were neither the elite achievers nor those who are struggling hugely.
Important to us is that our DCs are happy there and whenever we've discussed the possibility of leaving, mainly because of the expanding size of the school (and the school fees), they protest, as they largely enjoy everything and whilst they don't achieve with ease, they can 'hold their own'.
So a bright enough, fairly robust child can thrive there. An extremely academic/highly gifted child, with robust personality, would thrive even more. However, the school also seems to cater for children with specific issues, if this goes alongside intellectual ability - and to a degree, can cope with the milder end of 'emotional/behavioural problems'. So you'll always have the occasional child with certain problems - but this would happen in any school.
Overall, we would be happier if the school were half the size it is and with a better balance of female/male or instead, go back to all male. We've mostly had good experiences with staff, with the occasional issue with one - but again, any school will have some less than satisfactory teachers. We feel that the push for independence for the students is - most of the time - a positive thing and a good life skill.
We like the mix of families there - so that it's not it's definitely not 'posh/monied/snobby' dominated but has lots of ordinary hard-working families from a wider variety of backgrounds/cultures.
We have no direct experience of the Stephen Perse but have heard that it entirely depends on your child and the 'fit' with the school. I think that this school is also planning to go completely co-ed shortly. the smaller class sizes is appealing to many but this may change when the school expands.
OP, if I were you, I'd visit both these schools - and others, more than once on non-Open Days and also hang around in the car parks and get chatting to current parents but don't be swayed by the opinion of one or two. Also, remember that all schools are always in transition, as are these two and that your child's experience might be different from that of a child a few years ahead or behind.