I've heard great things about St Kevins - it's a Catholic school though? So if that is your need then it's a great option.
They are both good school. I write as a former student of CGS. I grappled with the two schools for my son and ended up choosing St Kevin. The latter is an incredibly sporty school and I felt my son would thrive in that environment. That’s not to say that Camberwell Grammar would have offered any compromise in sporting facilities because it was certainly very sporting when I was there 30 years ago.