^ That's basically my dilemma as well. I felt much more confident after coming out of my last test since I expected the curves to be higher.
I think that the tests in The Real ACT book were previously administered tests. Someone correct me if I'm wrong.
But anyway, I have a little theory that the ACT might be changing up its format a tiny bit. If you look at the early tests in the Red Book, the PDFs on the site, and other study guides, you can see that all of the problems are fairly accessible/ easy. The curve was usually -6 to still get a 30. However, with the new tests in the Red Book, the difficulty of the last 10-15 math problems were noticeably more difficult. The October ACT math section was similar to the ones I saw in the new edition of the Red Book, which is making me think that the ACT is transitioning over to a harder math section, but with a more generous curve.
Keep in mind that this is just a theory.