Well, speaking only for myself, it's clear that I'm not allowing myself to fully conceptualize the costs of a millenium of torture, even if I were able to, which I don't think I actually am.

But it's also clear that I'm not allowing myself, and am probably unable, to fully conceptualize the benefits of an immortal enjoyable life.

To put this more generally: my preference is to avoid cost/benefit tradeoffs where I can neither fully appreciate the costs nor the benefits. But, that said, I'm not sure that being able to appreciate the costs, but not the benefits, is an improvement.

Leaving all that aside, though... I suspect that, like you, I would choose to die (A) rather than choosing a long period of torture for someone else (B) if A and B were my choices. Of course, I don't know for sure, and I hope never to find out.

But I also suspect that if I found myself in the position of already having chosen B, or of benefiting from that choice made on my behalf, I would avoid awareness of having made/benefited the choice... that is, I suspect I am not one of those who actually walks away from Omelas.

I'm not proud of that, but there it is.