The verse of Blow The Man Down that refers to "I can see by the red-top sea boots you wear" followed by "robbed some poor dutchman of clothes, boots and all" seems to contradict itself! Unless he was carrying said articles in his sea bag, of course.
The "Blackball Line" shanty praises the ships and the sailors, whereas the version of Blow The Man Down (Blackball) does exactly the opposite, so I usually try to sing both versions, just to prove I am not biased:-)
I also do the same with "Santianna", doing the English(?) version praising the man, then doing the Yankee(?)(General Taylor) version, which is closer to the truth!
As to how fast a vessel could sail, that would depend mostly upon the strength of the wind, followed by the spread of sail and then by how trim the actual vessel was. But in this I defer to those who have got some "sea time" in. I am strictly a land sailor, and get sea sick standing on the quayside!