Modern cargo ships slow to the speed of the sailing clippers
guardian.co.uk
guardian.co.uk
But I doubt this will continue. The reason is the customers don't like it. If I have a billion dollars travelling from Shanghai to LA I want it to get there quickly so I can sell my product and use that billion for something else. This is why much-more-efficient-but-slower airships could never compete with airplanes.
If this is true, why don't we all just use sailing ships, which require no fuel and produce no emissions?
The standard deviation in speed would be high, and not all destinations could be managed on downwind courses.
All that said, the length of time the Cutty Sark held its speed record was amazing and inspiring. IIRC it took modern multi-hulls to beat it (sailing).