I haven't used this command (though I have used SetDccThrottle), but you can get a description of what to enter in the input table by going into CMP, finding the SetDccSpeed asset and left-clicking on it. A description comes up in the Asset Details box on the left. Atilabarut generally gives a good description of his stuff like that - wish everyone did.
I finally figured out how to use the Input/Table although it took some time. It doesn't appear to work for MPH in TR2010.
It may not be what I'm even looking for. I need a particular AI passenger train to ignore the speeds on the route and run a higher speed. I know I can set Invisible speed signs, but I need the Freight to run the posted speeds.
I was hoping there was something I could apply to the train itself and not the layout or track.
There is a driver command on the DLS called "Set Max Speed To" by nikkia. This allows you to set a maximum speed for any individual train or to vary the speed while en route to its destination. You could set the higher speed limits and restrict the freight by using this driver command.
I have virtually all my route is set with 30 Mph CSX Speedboards, as all my 12,000 Ton trainz are either fighting steep uphill grades, maxed out, crawling on their knees in Run 8 ... or are whining in full dynamic braking on a -2.37% downhill gradient ... aka: "The Slide".