Andy Murray DEFINITELY belongs with the other top 4 as far as ability is concerned. In fact, IMO only Federer is more naturally talented than him out of the 4.
However, there is a pretty big gap still between Andy and the other guys in mental ability. Let's be clear, since Lendl has come on board, Andy has cleared some pretty big obstacles, won his first slam, won Olympics by humbling Fed, finally beat Fed in a slam etc.
But I still don't get that "true champion" vibe from Murray, that "you can't beat me today no matter what you do" aura that I got from Fed,Nadal,Djoko when they were on their A-games. Even in the slam that he did win, I felt that Murray could've lost even after being 2 sets up. IN THE FINAL. That's a feeling you wouldn't normally get if the other 3 guys are in that particular situation.
So on that front Murray still needs to mature.