Depends on what iteration of Superman we're talking about. A lot of writers will argue his skill set is telepathy based, but he's unaware of it. If he were to become aware of his telepathic ability he'd be like Doctor Manhattan levels of godlike. When he stops a plane, he distributes the weight over the whole body instead of the single point of contact with his hand, otherwise the plane would crumble under the pressure of him trying to stop it. His heat vision is him heating up the particles in his line of sight, same with x-ray vision. Superman has a basically unlimited power ceiling, and it mostly depends on his emotional state - when he gets more angry he can do crazy things, we're talking about outrunning the Flash kinds of crazy things.