@Northernsurreyandconfused, we thought about the weekend sports fixtures too... a Home fixture sounds good, but it could be that the Away matches are closer to your actual home. We ruled St. Johns, Leatherhead out on that basis - 40 min drive from us.
Originally, I was keen on schools with coaches. Depending on the school, the coaches only depart at a fixed time after school - meaning that if your DS wants to do an after-school club, they'd miss the transport home and you'd have to pick him up, yourself. Some of the school buses pick up at 7am and don't drop the boys home before 6pm (depending on where you are on their bus routes) - a v long day, before they even think about homework.
The Esher-Guildford train service is pretty regular and part of the RGS social life - they meet each other, the Tormead and GHS girls. DS has friends at RGS that live in Walton, Esher, Weybridge. In some respects, the train is more flexible for them to do after-school clubs and the boys build more independence.
Good luck with choosing. Hopefully, you'll get a chance to visit the schools in person... and you'll see how much your DS is at ease and sense what he feels about the school. At Reed's, I had to push my DS through some doors to see what was on display (odd, as he'd played cricket and tennis there for 3yrs), whereas at RGS, he'd chat to the boy showing us around and get involved with the demonstrations. Still baffled why there was such a difference...