Yes, I think you're almost certainly right about the button, which thought does indeed put a dent in my lesser hesitation in choosing TORTURE. I think I would definitely not commit to not pressing the button if I were able to "try out" the SPECKS scenario for some short period of time first (say, a week). That way I could make a comparison. Absent that condition... I don't know. I can't imagine having the guts to commit to not pressing it.

The fact is that while I certainly don't see a momentary dust speck as torture, I can easily imagine beginning to see it as torture after a day, never mind 3^^^3 seconds, which is rather longer than 50 years. But I can't be certain of that, nor of to what extent I would get used to it, nor of how it would compare with much worse kinds of torture. (But then again, there's a spanner in the works: knowing that you won't have any lasting physical damage... perhaps that would lend some kind of strength of mind to a torturee?)