quality of study > quantity of study
You can really only do so much, natural ability is going to take over at some point.
agreed. you need to study to the point that you feel comfortable with the material. if you try to study more than everyone else, you will never be able to (there are some crazies in law school that will stop at nothing to get the top grades)
in my opinion, there is no way to gauge how you are doing compared to others until you get your grades. some students who seem like they have everything under control during class, may bomb the exam. like drbuff said you can only do what you can do, and from there hope that what you write in your exam is what the prof. is looking for.
Good luck on your exams!