One thing that has hit a nerve is 'good education' versus 'qualifications'. I have A+ qualifications from the state system, but feel I cannot write a decent letter, make appropriate conversation in some situations, have that inner confidence that private school colleagues seem to exude. I also have no debating skills or public speaking skills. These things all count for something.
Lemoning, I have read all through this thread with interest, and I was surprised to see you write this. You come across (in writing) as extremely articulate. I see no reason why you would be unable to write a decent letter, although obviously I can't comment on your conversation skills!
I do think that state school educated children can lack confidence. I certainly did. I went to a comprehensive and then to Oxford, and I spent a lot of the first year thinking I was thick, which I clearly wasn't. But I think that was at least in part down to my own personality. My brother went to the same comp, then on to vet school, and I don't think he had any confidence problems. That was just him.
And fwiw, in my small comp in the middle of Wales, I did debating and public speaking, and had all sorts of performing experience (in school plays and in local and national Eisteddfods). I'm a barrister now and am sure that all of those things helped me gain advocacy skills. These opportunities are available in the state sector, but you do have to look to find them.
I am now in London and committed to state educating my son and any other children we may have. I do understand why people want to give their children a private education (my husband was partly privately educated and is keener on it than me), but for me it is an awful lot of money for something that doesn't necessarily add similar value - unless your child has special needs that are difficult to cater for in the state sector. At Oxford, I didn't notice a huge gulf between the privately and state educated students.
On a different point, these Oxford admission stats may be of interest to you or your DH. In 2012, 28.4% of total applications were from comprehensives, compared with 26.1% of the intake. 16.5% of applications were from grammar schools, compared with 18.4% of the intake. The total number of applications from the state sector (including FE institutions etc) was 60.7%, compared with 56% of the actual intake. The independent sector had a better conversion rate with 35.5% of the applications compared with 41.5% of the admissions - but
as you can see, the figures are a lot less stark than the ones your DH gave you when you take the number of applications from each sector into account.
The link for these figures is here (click on the PDF for more detail): www.ox.ac.uk/about_the_university/facts_and_figures/undergraduate_admissions_statistics/
Many of the problems with state admission to Oxbridge (I'm concentrating on Oxford just because I know about it, not because I think either Oxford or Cambridge is the be-all and end-all) arise because parents and some teachers tell state school kids that it's not for the likes of them. I think this is sad, but to be blunt, it's not something that need bother you because clearly you and your DH have great ambition for your children.
I don't know whether any of this rambling helps, but good luck with making your decision. I understand that this is not easy.