Just thought I'd comment that the more I think about the question, the more confusing it becomes. I'm inclined to think that if we consider the max utility state of every person having maximal fulfilment, and a "dust speck" as the minimal amount of "unfulfilment" from the top a person can experience, then two people experiencing a single "dust speck" is not quite as bad as a sigle person two "dust specks" below optimal. I think the reason I'm thinking that is that the second speck takes away more proportionally than the first speck did.

Oh, one other thing. I was assuming for my replies both here and in the other thread that we're only talking about the actual "moment of suffering" caused by a dust speck event, with no potential "side effects"

If we consider that those can have consequences, I'm pretty sure that on average those would be negative/harmful, and when the law of large numbers is invoked via stupendously large numbers, well, in that case I'm going with TORTURE.

For the moment at least. :)