I think I'd agree, Codger. The sheet music from the Scottish Students' Song Book has the whole song marked allegro, so I set a quarter note at 140 beats per minute. That's a bit slow for the verses, but it's breakneck speed for the chorus (if sung as written). I think I'd sing the chorus quickly, but not THAT quickly.

And yes, I've often noticed that the authentic chantey singers sing a lot slower than them college-educated city boys that show up at chantey sings on the weekends....

-Joe-