I've had my share of roomates over the years. From potheads to regular students to bums with no job crashing on the couch (yeah its a bitch when the rents due). So I decided to go without. Although it had nothing to do with my performance or their performance in school.
I could care less what other people are getting and I dont tell anyone what I get on tests/courses. If they ask I always say I did "alright" and they can take that to be whatever they want.