murray has a slam final, the latest one. he is in incredible form, taking the standard of tennis to new heights.
True enough, but one hasn't truly "arrived" until they get that first slam title under their belt. Murray IS the man to beat right now but I think he still has a little ways to go to prove himself.
But for the sake of your thread, I'd say that Gulbis stands the biggest chance of turning a "Big 4" into a "Big 5". Just a guess. Then again, there are plenty of other guys who could just as easily be as successful.