First, I firmly believe you get just as much benefit from doing customized MCQ and SIM test banks as you do from tests. I usually only do tests to see how my timing is.
I'm pretty sure Wiley has each section weighted the same (approx. 20% each test section). There is no partial credit on SIMS and the program evenly weights the answers within the SIM (i.e. 5 question prompts = 20% each question). This is what I have concluded from using the program for all four sections in the past year. I'm no expert and could likely be wrong, but this is my experience and opinion.
I track all of my practice exams and MCQ/SIM customized test banks. I don't have my AUD (passed, 86) or REG (passed, 82) stats anymore, but I do have BEC and FAR.
For FAR: I took 1,178 practice MCQs and 87 SIMs prior to test date. My median percentage on MCQs was 66.7% and for SIMs was 78.5%. On test day, I recognized many questions and felt as if Wiley had given me A LOT of the “harder” level MCQ questions during practice. I felt like my second MCQ testlet was the harder level. I felt prepared for SIMs, even though you never know for sure how well you did. I didn't feel “beat-up” after the test and I'm excited to see my score.
For BEC: I have taken 896 MCQs and 30 SIMs. I have a median percentage on MCQs of 80.6% and 89.0% on SIMs. I feel confident with the material and I sit for my exam on 9/7/2018.
Sorry for the long post…good luck!