@cev
To me, the difference in FAR was obvious because the questions changed in so many respects. Most of the questions were on topics that are generally considered tougher based on what I read in my review text and this forum. The calculations were more complex in that they either required more steps to reach the answer or you had to figure out the answer from information that initially didn't seem to be sufficient. Also, the questions were often wordier so they took longer to read and required you to determine what was the needed info and what was superfluous.
With AUD there was a change in topics, but they weren't more difficult ones IMO. The calculation factors from FAR weren't applicable since AUD is almost all theoretical questions. Also, I didn't notice a big change in the length of questions.
My first two MCQ on REG were really tough so that probably influenced my perception of the difficulty factor of the first testlet as compared to the other two. I honestly don't remember much about the MCQ because the SIMS blocked everything else out.
Again, on BEC, I don't know which topics were supposed to be the toughest so I couldn't judge from that perspective. I felt like I did well on the first testlet so I assumed that the next one was considered more difficult by the AICPA, but I didn't notice a significant difference. The third one might have been a little harder but not by much.
FAR 4/1/11 - 89
AUD 4/15/11 - 85
REG 4/29/11 - 80
BEC 5/13/11 - 85