Well, first of all, I'm assuming that you're doing that to both groupings (since otherwise I could say "Well, one has only one person and one has a massive number of people, which is a difference." but that seems like a trivial point) So if you apply it to both, then it's just one person considering tradeoff A, (pay torture to go speck free for eons) And another person considering tradeoff B(personally build pyramids for eons to get to live in your own collection of pyramids for some years.) I could say that in once case the pain is relatively dense (torture, condensed to 50 years) and the pleasure is relatively sparse,(speck free, over 3^^^3 years) and that in the other case the pain relatively sparse (slave labor, spread out over a long time) and the pleasure is relatively dense (Incomprehensible pyramidgasm.). I'm not sure if that matters or in what ways that difference matters. I'm really not up to date on how your brain handles that specifically and would probably need to look it up further.

If I understand the dilemma, in your most recent phrasing, it's this: A person who lives 3^^^3 years either: a) has to suffer a dustspeck per year b) has to suffer 50 years of torture at some point in that time, then I assume gets the memory of that torture deleted from his mind and his mind's state restored to what it was before the torture (so that he doesn't suffer further disutility from that memory or the broken mind-state, he only has to suffer the torture itself), He lives the remaining 3^^^3 years dustspeck-free. If we don't know what his own preferences are, and have no way of asking him, what should we choose on his behalf? But what does this have to do with Felix?