Fastest passenger ship in the world?

The Queen Mary 2 is the fastest ship soon to be in service with a top speed of 33 knots, however, the fastest of all time is the SS United States which still holds Atlantic crossing records and known top speed was 44 knots. There has always been speculation that this figure was sandbagging and the actual top speed was higher but classified by the U.S. Government. The Big U is awaiting decisions on its fate in a berth on the Delaware River in Philadelphia, PA and is currently owned by Norwegian Cruise Lines.