What monitor resolution?
Dishonored isn't a resource hog, you shouldn't be having issues with that one.
Im playing at 1920x1080. I played Dishonored again today and had not a single problem. Not sure if it matters, but the last time I was playing my son was streaming some video from my computer using the PS3 Media Server. But when I played for a couple hours today, there was not a single problem.
Borderlands 2 on the other hand I had issues with. I wasnt running any framerate checker, but it dropped to probably 15fps at times. And I dont even have my setting set to high.