Extreme pain induces perhaps the strongest emotional bias imaginable; aside from simple sadism, that's the main reason why torture has historically been practiced. Knowing this, I'd hesitate to give much weight to my assumed preferences under torture.
More generally, wishing for death under extreme emotional stress does not imply a volitional desire for death: that's the assumption behind suicide hotlines, etc., and I've seen no particular evidence that it's a mistaken one.
I would press the button if I estimated that the uploaded copy of me stood to gain more from the upload than the copy of me being uploaded would lose in the pain of the process. The answer to that question isn't explicitly given as a premise, but with "effective immortality" to play with, it seems reasonable to assume that it's positive.
Knowing this, I'd hesitate to give much weight to my assumed preferences under torture.
You're not asking yourself whether you'd like to die, all things being equal. You're asking yourself whether you'd prefer death to the torture. And you would--the "you" that was undergoing the torture, would.
If you could gain immortality by subjecting someone else, a stranger from a different country, someone you've never met, to a thousand years of torture--would you do it?
I would not.
I have been trying to absorb the Lesswrong near-consensus on cryonics/quantum mechanics/uploading, and I confess to being unpersuaded by it. I'm not hostile to cryonics; just indifferent, and having a bit of trouble articulating why the insights on identity that I have been picking up from the quantum mechanics sequence aren't compelling to me. I offer the following thought experiment in hopes that others may be able to present the argument more effectively if they understand the objection here.
Suppose that Omega appears before you and says, “All life on Earth is going to be destroyed tomorrow by [insert cataclysmic event of your choice here]. I offer you the chance to push this button, which will upload your consciousness to a safe place out of reach of the cataclysmic event, preserving all of your memories, etc. up to the moment you pushed the button and optimizing you such that you will be effectively immortal. However, the uploading process is painful, and because it interferes with your normal perception of time, your original mind/body will subjectively experience the time after you pushed the button but before the process is complete as a thousand years of the most intense agony. Additionally, I can tell you that a sufficient number of other people will choose to push the button that your uploaded existence will not be lonely.”
Do you push the button?
My understanding of the Lesswrong consensus on this issue is that my uploaded consciousness is me, not just a copy of me. I'm hoping the above hypothetical illustrates why I'm having trouble accepting that.