Zodiac is one of my favorite films, Mexicola, and I've seen it numerous times, but I'm not a fan of the violence in it. The stabbing scene being the worst, so I agree with you about that. The other scenes I just close my eyes, but I know where you're coming from .
I have trouble watching anything where people are tortured or impaled on things, yuck. I'm not a fan of gore so if there's blood it it has to be quick and fleeting otherwise I just shut my eyes.