x amount of suffering is just as bad, i.e. that we care about it just as much, in nonhuman animals as in humans, or in aliens or in uploads.

By this I meant literally the same amount (and intensity!) of suffering. So I agree with the point you and Carl Shulman make, if it is the case that some animals can only experience so much suffering, then it makes sense to value them accordingly.

You must either 1) assign gradually diminishing moral value to beings ranged from humans to amoebas; or 2) choose an arbitrary, precise point (or several points) at which the value decreases sharply, with modern species boundaries being an obvious Schelling point but not the only option.

I'm arguing for 1), but I would only do it by species in order to save time for calculations. If I had infinite computing power, I would do the calculation for each individual separately according to indicators of what constitutes capacity for suffering and its intensity. Incidentally, I would also assign at least a 20% chance that brain size doesn't matter, some people in fact have this view.

I don't understand what you mean by (2), could you give an example? If a utilitarian calculation forbids you from doing something, then what could be your reason for doing it anyway?

By "utilitarianism" I meant hedonistic utilitarianism in general, not your personal utility function that (in this scenario) differentiates between sapience and mere sentience. I added this qualifier because "you'd have to be okay with torturing babies" is not a reductio, since utilitarians would have to bite this bullet anyway if they could thereby prevent an even greater amount of suffering in the future.

Please play rationalist's taboo here. What empirical test or physical fact tells you whether "it feels like something" to be a certain animal? And moreover, quantitatively so - "how much" it feels like something to be that animal?>>

I only have my first-person evidence to go with. This bothers me a lot but I'm assuming that some day we will have solved all the problems in philosophy of mind and can then map out what we mean precisely by "sentience", having it correspond to specific implemented algorithms or brain states.

Baby-ism and racism have nothing in common (except that you're against both). I don't assign human-level moral status to babies, but I'm not a racist. This is precisely because humans of all races have roughly the same distribution on A-G (and other relevant parameters), whereas newborn babies would test below adults of most (all?) mammalian species.

I agree, those are simply the two premises the conclusion that we should value all suffering equally is based on. You end up with coherent positions by rejection one or both of the two.