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Robin Stuart you wrote: I revisited the Charles Lindbergh’s Great Circle Chart https://www.wdl.org/en/item/6778/ that David Pike had drawn attention to in his post http://fer3.com/arc/m2.aspx/Great-Circle-Sailing-Chart-DavidPike-jan-2016-g34267 Lindbergh’s great circle from New York to Paris is obvious but one can also see the some of the lines that were used in intermediate steps.

I think you meant my post http://fer3.com/arc/m2.aspx/Great-Circle-Sailing-Chart-DavidPike-jan-2016-g34228 .   I look forward to reading the remainder of your post later.  Daylight and dryness is at a premium for outside work these days.  Regarding statute miles.  I think it's just what aviators used until after WW2.  Spirit of St Louis's airspeed indicator was definitely statute mph https://airandspace.si.edu/collection-objects/ryan-nyp-spirit-st-louis-charles-lindbergh (you might need to fiddle with this to get it to enlarge).  Also, for a record breaking attempt the media and sponsors were more likely to understand statute miles.  DaveP