Right so it seems you are on the correct drivers. Just going back and re-reading the thread I think I see your problem.
Its not a given that a 4850 is not automatically better than a 8800GT. It depends on the game. As these cards are quite old most reviews wont include them. Some specific tests for BF3 exist and they have the cards about neck and neck.
The issue you are having is that the Mobile 4850 is about as good as a standard 4830 and not as good as the standard 4850, which is where I believe your performance expectations are falling down.