I actually took the test today as well and agree that the SA portion of the test is a lot harder than the practice ARCO books. I took the ARCO practice test once w/ a timer and only missed 1 with 3:00 minutes left. I finished the whole SA section on the ASTB but ended up missing around 5 or so.
Just FYI, I took Form I and that monkey problem was on it...very glad I read this thread before taking it
Also, the practice ASTB on this site is very very similar to the actual test. In fact, they mainly just change the numbers and situation around. If you are about to take the ASTB, study the practice test (PDF file) on this site and make sure you understand every problem. Don't waste your time with the ARCO book except to get a feel for the SA section, it's totally worthless (the questions on the ARCO test are much harder than the actual ASTB while the PDF on this site is almost identical)
Unofficial scores 7/7/6 OAR 57