you should prefer torturing someone for six hours and them killing them to letting them contemplate their imminent death in comfort for six hours and then killing them

When you're being tortured you have no choice but to attend to the pain: you are not cognitively free to contemplate anything other than your own destruction. In comfort you could at least aim for a more pleasant state of mind - you can make your own plans for those six hours instead of following the torturer's, and if you have the strength, refuse to contemplate your own death.