My DC are very young, but DH and I have already talked about this. We both went to Oxbridge and have a LOT of high-achieving but really very stressed and unhappy friends - no achievement is enough, and they feel something undefinable but crucial is missing from their lives.
DH and I are both working in fields directly related to our degree subjects (which were a passion for each of us), but which are not high-paid (although perfectly good enough), nor high-flying/glamorous. We are both extremely happy, and feel a sense of fulfilment in what we do, which is wonderful (I changed career in my 30s, after being much more high-powered, but rather unhappy).
With that in mind, we believe very strongly that it is important for our children to really enjoy their school years, to have a well-rounded approach to learning, and to pursue learning because of an inherent love of it. The primary school we have chosen fits that bill. It's small, friendly, with a strong focus on pastoral care, good manners, and a wide range of activities. The two who are there currently absolutely love it, and go off every day looking forward to their activities. The school also gets very good results, as it happens.
We've begun looking round at secondary schools. At the moment, there's one in particular we're favouring. It doesn't get the best results in the area (although every year some children go to Oxbridge/med school etc. However, again, it has a strong focus on pastoral care, extra-curricular activities, music, drama, sport etc.
I see absolutely no point in taking GCSEs/A-levels early. Far better to spend extra time on a wider range of activities. One of those might turn out to be a driving passion that is really important for future happiness.
It's early days for our DC, but we think they are bright. We also believe that we have the capability to notice if they are falling behind their academic potential, and put in measures to help them. We want a school where they will flourish, be really busy, interested, and productive, and enjoy themselves hugely. I think good results grow naturally out of that sort of environment, and more importantly, so does lifelong satisfaction.
(though perhaps I'll be back in ten years time, with completely different views, it is still early days)