I took my boards at the end of January (160 questions). I thought it was a difficult test. I felt like I was prepared, but after getting 160 q. my confidence was shaken, as you can imagine. Fortunately I passed...
This is what I studied (besides the 'core' literature, e.g. Barash, etc.) and what I recommend:
NA Handbook (Nagelhout)
Good review of diseases and surgical procedures.
Five simulation tests with links and explanations, computer based.
R&R (test book only)
Another review course. The book has tests that are good for general systems info (cardiac, renal, endocrine, etc.).
Anesthesia Secrets by James Duke
Covers anesthesia concepts.
Good luck, I hope you passed!