I moved my son to St George's from a local state school at the start of Year 9/Third Year two years ago because he loves maths and science, and those subjects were really being dumbed down where he was. He is thriving - loves the challenge and although he is a bit of an eccentric at times, he has fitted in well. He is not at all sporty but seems to manage anyway. I have been impressed by the change in him (he was getting lots of detentions for forgetting homework and basically disengaging at his old school) and the support from the staff who seem to know what he is capable of and won't let him get away with anything, but don't make him stressed either. Communication seems good. I can't compare to Reeds as we didn't look at it. Good luck with your decision!
If you do a search there are various threads about these two schools. Ds goes to Reed's which we are very happy with. He is in the Third Year (yr 9) and all our experiences with the school have been very positive. We didn't look at St Georges though so I can't compare them. You can pm me if you have any specific questions.
My dd was at St George's but has moved for sixth form. There are a lot of smokers there, children hide in the big grounds, although some of them have bravado and smoke at the front of the college. Also a pair of students were caught last year having intercourse in the grounds. Academically they do well for GCSE's but A Level is a disaster. They do have a lot of activities to keep dc busy. I dont know anything about Reeds.
My DSs went to SGC. DS1 loved it, DS2 less so. DS1 did well academically; DS2 is not a natural student and they pushed him as much as humanly possible.
It's a well run school, but the Head is a bit pompous. They do well because they are in an area with a drought of good state schools and few independent schools for boys.
I didn't choose it for my DDs .
SGC has a more academic intake than Reeds (Reeds will take those who narrowly miss the SGC pre-test). It has a good reputation for pastoral care, dealing well with students from sensitive family backgrounds.
Both schools are good schools. You could make your choice on which school is easier to get to.