I think it probably is possible for medical researchers to arrive at some reasonable estimate of the degree of pain likely to be associated with different ways of dying, though of course it's very difficult to compare one person's experience of pain with another's even when they're suffering the same trauma.
Well I don't know if I would agree with "probable" as all of our current methods rely on monitoring the electronic impulses thru the nervous system and our interpretation of how the brain works (an organ we really don't understand). I would agree that they can draw some conclusions based on our current knowledge. But conclusions are not facts.
Your point about pain being relative is extremely important. I find pain erotically stimulating, I have a sister-in-law who if she has a headache is convinced she is dying.
Of course, the moment of death is itself necessarily the end of any pain.
Well that is just a guess, one which most of the major religions religions that exist (or have existed) would disagree on. The concept is called Hell in English and it is pretty universal.
One of the Nazis' contributions to scientific knowledge was tying up naked prisoners on beds and leaving them outside through freezing cold nights to study the medical effects.
The Nazi's faced even more limitations on the subject than we do because their medical technology was less advanced.
One of the problems in all of this is we look at a "result" and even if we know the "cause" (freezing to death) we guess about a good deal of what is going on. In order for it to be scientific knowledge it has to be measurable and reproducible. And even if we can measure things (like a reduction in brain activity) what is going inside the brain (feelings, delusions, etc) is merely a guess on our part.
All through out history some of the latest "scientific" knowledge has had a really bad habit of becoming tomorrow's scientific nonsense (You can't create a heavier than air flight machine, you can't exceed the speed of sound, set off an atomic bomb and you'll start an uncontrolled chain reaction that will destroy the world, just to name a very few recent ones).
But the arguments are great fun until they become fact.
kisses
willowfall