I do not know about the ceiling or which test to take, but can weigh in on the questions...it is a CAT (computer adaptive test) much like the gmat. It is extremely important to get the first few questions right so that you can get to the harder questions at the end. With every question you get correct, you get a harder question.
The way I think about it is that the first questions determine the general range of score and the last questions determine the exact score within that range. I always coached dd to take all the time she needed at the beginning and that she knows she did well if she got to really hard questions at the end.
