I don't really understand what benefit there is to the mental catagory of impossible-but-not-mathematically impossible. Is there a subtle distinction between that and just "very hard" that I'm missing? Somehow "Shut up and do the very hard" doesn't have quite the same ring to it.
Whilst the your analysis of life-saving choices seems fairly uncontentious, I'm not entirely convinced that the arithmetic of different types of suffering add together the way you assume. It seems at least plausible to me that where dust motes are individual points, torture is a section of a contiuous line, and thus you can count the points, or you can measure the lengths of different lines, but no number of the former will add up to the latter.
This reminds me of when I first started learning about topological spaces, and then we added a metric, suddenly all the theorems and lemmas we'd had to prove in fiddly ways with lots of epsilons and deltas in first year analysis were blindingly and beautifully obvious. The sheer glorious interconnectedness was so overwhelming that I very nearly orgasmed in the lecture theatre!