We were in a similar position to you last year. We live very near to MGS and can walk there in 15mins, but my DS wanted Judd. I found it a very difficult to chose between the two. For several reasons we felt MGS was not right for him but Judd seemed perfect, the only negative being travel, which for mgs was a positive. I let my ds choose in the end as he was adamant he wanted Judd even though he wouldn't know anyone as his friends chose Maidstone schools.
We don't regret the decision one bit, he is very happy, coping fine with the journey and loves going to school.
I wouldn't choose Judd just because of a high score but would consider how the child may fit in as a whole, as the chances are he could possibly go from being top at primary to bottom in a superselective, so some children may cope better at MGS as there is a broader range of ability. My ds was highly able in primary and the teachers struggled to challenge him, which he found frustrating so we were confident he would flourish in a high ability environment. He is also not bothered if he isn't always top of the class as he was growing fed up with some of the unwanted attention it caused at primary. But some children would struggle with this and lose confidence.
What I'm trying to say is try not to be seduced by what may appear to be the best school because that may not be the best school for your DC. Think about the big picture and how your ds will cope for the next seven years. Also consider after school clubs and sporting fixtures as these will affect travel times.
If you have any questions feel free to pm me
We didn't consider Skinners as I felt that was too far to travel. Not keen on the Blazers either.