I did noticeably worse on SC on GMATP2 vs. 1, but ended up w/ 730 overall for both. I really think concentration has a lot to do with it. For example, when my confidence was getting too high, I started to listen to my ear more instead of really analyzing and identifying the reasons why each answer choice were wrong. This is obviously a no-no, except for idioms, but is easy to do when you are pressed for time or over-confident and "lazy" or sloppy.