I'd say FSA on that BSAS was as hard or harder than i've seen on anything that i've taken- including the dec CFA test.
Book 7 is a pretty good judge I'd think. Book 6 maybe is a little easier than the real thing, but it's a pretty good indicator also. Honestly, though, I could have 80's on all of these and have a panic attack come test day and bomb. Or, maybe you just get lucky on test day and get a bunch of q's you're good at. Study as much as you can, get as many points as you can, worry less about your practice test scores and more about learning the stuff you got wrong so you don't make the same mistakes come test day. I think that's the only advice. When you walk out of the test in a few weeks, you'll have a good feel of whether you passed or failed. If you're doing book 6 and 7, you won't be blown away by the test, but it's going to stretch your mind in ways it probably doesn't want to be stretched all in one day. Keep going, study more, worry less about a 67 vs a 72% on book 7 tests.