Also have a DS in yr7 at WCGS. I think you need to look at your sons personality a bit. There was something about SG & Wilsons which was quite wrong for my DS and it's very difficult to put a finger on what that is. A good friend of his has gone to SGS and I can see that it's very right for him, indeed I know quite a lot of boys at SGS and all are very happy there.
From my own experience - WCGS have an excellent induction process.
Totally agree - forgot about the induction days - DS didn't want to go back to his primary school afterwards!