FAR is long because a lot of questions require a lot of extensive calculations. AUD is long because the questions require a lot of analysis. Misreading one word can throw you off and make you pick the wrong answer. So, trust me when I say that 4 hours is just enough time for AUD. If you finished AUD in a short amount of time, then chances are you made some careless errors even though you passed.
Now REG is short because the questions don't take a lot of time to solve. You either know it or you don't. The calculation questions are only simple additions and subtractions. It WHAT you add and subtract that is the hard part. But if you know your stuff well, I can see some people finishing in less than 3 hours.
FAR: 52, 66, 73, 61, 89
AUD: 47, 87
BEC: 80
REG: 64, 74, 84
DONE!!!!