I'm not going to get into Cambridge!
My son was in an independent which was rubbish and a two others I didn't like, although I could see they had some positives!
My sons were also in a really nice state primary and the Head tried to do her best my DS1 but she didn't have the resources. I would send another child to that school without any concerns until Year 3 and if I couldn't afford independent school, then for longer. I would also be comfortable with GS schools depending on the area they were in but if I'm honest I wouldn't send my son to a comp and would home-ed instead. I know some faith comps are good but we wouldn't get in.
I was bullied for being bright at my sink school (it is a sink school still) and I don't care what anyone thinks but my son would get slaughtered at a comp. When you see really bright kids on TV
, you think Oh My aren't they weird - and we're intelligent adults who think like that, so how much worse would their peers treat them!
So, I suppose it all depends on the kids and some kids don't benefit from an independent education, and some really need one.