OK here comes the real facts...
It is now known that the SS United States achieved speeds exceeding 44
knots, or 50mph (footnote by the SS United States Foundation).
I found the power curves for SS United States here:
http://www.ss-united-states.net/SSUnitedStatesWebpageFiles/WebPages/PagesHP.htm (http://www.ss-united-states.net/SSUnitedStatesWebpageFiles/WebPages/PagesHP.htm)
As the notes point out, it would take considerably more power to reach even 40 knots, let alone 44.
44 Knots is about 1.25 times her service maximum of ~35 knots. It would require at least 1.58 times the power to reach that speed. It is unlikely that a liner designed for 35 knots would have a 60% power reserve. The extra boiler capacity alone would have been unjustified from an economic standpoint.
The US Navy, who paid the majority of her cost, and supplied the propulsion technology, maintains that her maximum speed in trials did not exceed 38.5 knots. The 44-knot speed was an exaggeration that gained credence through parroting, as many of the Titanic myths did.
The SS United States Foundation is a group of dreamers trying to raise money for a project with as little chance of success as the plethora of plans to launch another Titanic. They are hardly a reliable source of information. A site that, in a footnote, cites itself as an authority is humorous. If you look at their latest news page, it is dated January 11, 2007.