78/ 3100 state secondary schools! I give zero credence to league tables anyway, your child, his peer groups, his particular teacher during a particular term, are all more likely to effect his end results than whether the school is 50 places higher up the league table. Top 100 schools have very little between them in the most important, and seldom published figures, which is how much each individual child has achieved educationally higher than when they started. Also please remember that dcgs, although unquestionably also a great school, is situated in a very affluent area, where the slightest sniff towards a c grade sends some (certainly not all) parents running to private tutors with their teens....says she who is looking at French tutors for ds1, even though we are cash strapped!
Also just think, the extra two hours commuting could be spent doing fun exercise and energizing his brain or doing extra booster work if need be, as well as relaxing at hone!
Good luck, and set that basketball hoop and tennis net up in the garden to get him ready over the summer...great fun!