Yeah, I think it's a non-issue, really. Vulcans don't have to be "fair," just logical. If the information is extremely important and time is of the essence, logic could dictate that rendering the subject unconscious is necessary.
Of course, you also have to consider the dramatic importance of the situation, and a good Narrator would give out extra experience for characters who enhanced the drama of the episode/encounter (like Spock's interrogation of Valeris in ST VI).
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz