12-hour sweep hour hand for 3918.18.LBK8, 3918.19.LBK9, and 3918.196.LBK7F
24-hour sweep GMT hand for 3918.18.LBK8, 3918.19.LBK9, and 3918.196.LBK7F
24-hour sweep hour hand for 3918.18.66.LBK8, 3918.19.66.LBK9, and 3918.196.66.LBK7F
So for the GMT version, it's only the GMT hand that sweeps a 24hrs revolution. I prefer that as I think it's easier to read the time on a 12hrs version, esp with the already complicated dial and bezel complication.
You can also see this video, just past the 10mins mark, where the reviewer talks about how to read the time on the GMT piece -
https://www.youtube.com/watch?v=AxYVfC18Sds&t=494s
AurochAre the movements between the purist and the GMT exactly the same? I would feel like something is being underutilized if the purist was just the regular GMT model movement, but they placed the hour hand on the axle that would normally power the GMT hand. Internally there is still something clicking away inside the movement showing the hours in 12hr format--there's just no hand attached to this part of the movement. Seems like wasted energy and for this reason I would go with the GMT model even though the purist model looks cleaner and has the unique 24 hour display for the hour hand