Re: Vulcan Fairlie top speed and livery question

The build dates might not rule them out being related designs. There are other cases from that era of engines built decades apart using the same construction drawings.

As to the livery, I don't know. I do not know standard practices for the English firms in that era. I trust your word on that.

Where did that paper originate? Both the weights (gross tons vs. net tons) and water tank capacity (U.S. vs. Imperial gallons) might not mean what they seem to mean.
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Speed is hard to discuss in any absolute sense with respect to steam engines. Steam engines don't necessarily have a singular "top speed" in the same sense that an automobile governed at 106 MPH has. They don't work that way. Effective top speed--especially on narrow gauge railroads in the 1870's--usually amounts to how fast you think you can go without leaving the rails. The majority of railroads during the "iron rails" era did not want to run particularly fast due to track damage incurred. Otherwise your top speed is going to be limited either by how much power you can make versus the load you're pulling (more load = lower achievable speed), or ultimately by how fast you can go before the locomotive breaks itself. You might run up to 400, 450, even 500 RPM once as a PR stunt, but try it day in and day out and you'll find yourself breaking things at a rapid rate. Even the famous, modern A4 "Mallard" broke itself on its record run.

Track wear aside, About 300-360 RPM was a good value for what you could do in normal service without incurring excessive wear to the machinery. Many railroads were happy enough cruising at half that or less until the adoption of steel rails. The D&RG of the 1870's was happy enough running freights at 8-12 MPH and passenger trains at about a 20 MPH cruising speed. Elsewhere you can find railroads that ran faster. NZR ran faster but it used steel rails early.

Obviously you can go faster with a given load downhill than uphill.