Newbie - you should take a look at Cranleigh School. Ds is there - v happy. They cater for a broader cross section, but cannot remember pass mark at Common Entrance - it was about 65%? Its co-ed, day and boarding.
Both DS1 and DS2 are at RGS and both love it. It is quite academic and the boys who are at the top of the class are REALLY academic. My DS2 was invited back to sit the scholarship exam and he is currently in the top half of his class, but only just, so there is quite a range of abilities even if your DS does get in! I'm with the other contributors that I'd have a ponder if your DS gets called back for a second interview as those boys generally do struggle initially (unless the exam day really was an 'off' day). For what it's worth, I know a number of boys who have gone at 13 and regretted not joining at 11. At 11 all the boys are new and they form firm friendships which seem to last the length of their school career. They also have time to 'have fun' whereas at 13, they've toiled for 2 years in their prep schools to take the 13+ and then they have to go straight into Year 9 when the boys really start to knuckle down. To me it's a no brainer... Sorry - dont know anything about Churchers but I have heard good things about it!