Another thing that might help a potentially tight simulation is using the additional cloth collision options (object vertex on cloth polygon, object polygon against cloth polygon). It makes the simulation take longer, but in my experience, even my slow computer handles it okay. (I've only had problems with objects with really, really high polygon counts.) As I understand it, those two options are different ways to double- and triple-check each frame of the simulation to make sure the cloth doesn't get too close to the collision objects.