Investigating further, I find there's (as far as my ears can tell) exactly half a tone's difference between the two: Suibhne's recording has We Have Fed Our Seas in C and Sir Patrick Spens in E, where Itxlan's has them in B and Eb respectively. My speculation that the original pitching (and speed) might have been somewhere in between the two seems to have been disproved - there isn't anywhere to go in between.

Wonderful stuff, although (as you can probably tell) I'm having to get used to the slower pace and deeper pitches!