I am sure you are already doing this - but ask yourself really honestly if Marling or Crypt are really so much better than the school your son would be going to anyway. Enough to warrant this kind of journey for the next six years, day in, day out.
Yes, I have done nothing but think about the whole situation. The problem is Bristol schools are not on the same standard as Gloucestershire schools. We are not in the catchment of a good comprehensive or academy. I went to Crypt and asked the same questions and got the same replies you all gave me. My husband and I have decided to move after we know ds allocation. I will have to commute to Bristol for work. Our new problem will be getting a good primary for dd in Cam/Dursley area.