Well, I don't know. As Lazarus and Cyph have reinforced again and again, the scaling tends to depend on the candidature and the difficulty of the course.
Subjects that seem to scale Really well are the following:
Extension 1 and 2 maths
Extension 1 (?) and 2 English
Physics
Chemistry
Latin
Extension subjects
Distinction courses
Subjects that scale reasonably well:
Language continuers
Advanced English
I am not too sure. I think Cyph has posted the scaling list somewhere