How long ago was the Outstanding school inspected? Lots were years ago and this rating may no longer be relevant if a lot has changed in the meantime. There is little to choose between Outstanding and Good. The Good may still be getting better. Check where the Good school needs to improve and ask them if they have improved in these areas. Tell DH that Outstanding isn’t necessarily Gold standard if the inspection is way out of date.
In Good schools, many of the pupils will achieve just as highly as in an Outstanding school. Check the most recent data such as progress 8 on the government’s web site. Where do the schools rank in comparison to other similar schools? What are their average scores/grades at GCSE and A level? All this info is available.
Is the Outstanding school doing lots of extra classes to push up results? Is this what you want? What are the results for middle and high achievers? Are there noticeable differences and which school has most of each category? What are the strengths of the Catholic school? Get your DS to articulate them as opposed to just saying his friends will go there. Also universities don’t care what school you went to unless it’s on the list of schools where they give lower offers to applicants. Bristol university used to publish their list.
As you are Catholic, I’m surprised your DH doesn’t agree to Catholic. Most Catholic parents like the ethos that I know. I honestly doubt that your DS would be failed by the Catholic school although going with current friends isn’t the best reason to choose it. Friends find new friends! Also if he’s sporty, do it out of school and join a club. If your DS will hate not winning he might regret not going to the bigger school but if he does sport elsewhere it won’t matter so much.
It’s very difficult to avoid conflict in the family but DH is being a bit unreasonable. It’s not as if the Catholic school is RI or worse! However if it’s dipped into these categories in its history, then I’d be a bit concerned. If it’s solidly Good, I’d be less bothered. Do you trust the Head to keep the decent teachers? Does it feel purposeful and have the breadth of education that would suit DS? If it does, that’s useful ammunition. If it is small because no one wants to go there and it has loads of unfilled places, I would worry a bit. Is it filled to capacity? Hope some of this helps!