Hola TJ -
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The names and definitions you have there, transcontinental, transatlantic and transpacific are somewhat arbitrary...
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I suspect these definitions were mostly used in the UK/USA aviation community. Generally, in the USA, they mention transcontinental as being a coast to coast flight (i.e. NYC to SFO), transatlantic being in the mind of USA people a NYC to LHR or CDG flight, and transpacific is a typical SFO to TYO flight...
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But in airline operations practice, some other considerations.
As a pilot, I use nautical miles for these distances.
From YQX (Gander) to SNN (Shannon) the air distance is 1,850 NM to cross the ocean... yet distance from NYC to London... is about 3,000 NM.
From SFO to HNL (Honolulu) the air distance is 2,300 NM...
From SFO to Tokyo, transpacific, you are looking at some 6,000 NM...
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So be arbitrary too. For me transcontinental, means some 2,000+ NM...
Transantlantic means 3,500+ range capability...
And for transpacific, how about 6,000+ range...
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Hope this helps -
Happy contrails
P.S. - For me, living in Buenos Aires, a transatlantic flight is a very long flight, as flying to Madrid from here is generally 11 hours long... So honest, no solid definitions... Shall we talk "transpolar" as well...?