Anand,
You should also note that some mock exams are harder than others.
I know content differs a bit and it might be a function of gaps in my particualt knowledge...but I have scored much lower (15-19 percentage points) on Dan Chisholm's mocks than I did on Marcus Green/K&B CD exam/Sun ePractice exam.
That's not to say that you shouldn't do Dan's mocks as well, as they really pushed me...or that the others are not hard enough, because I don't think thats the case either.
Anywise, if everytime you get a question wrong you discover the reason why then that is a good thing.
Good luck.
Cheers,
Si.