Based on the 10 released NBMEs, the biostats questions that they like to ask are pretty well covered by First Aid/UWorld. I mean you do see some weird questions, but those happen with every subject. I'd think if you know First Aid cold you should be pretty confident in most things that they can throw at you.
I think First Aid psych is more than enough. Psych is one of the most straight forward of the "behavioral sciences" type questions that you can get. I'd consider myself lucky if all of my questions were from that category. There are a few diagnoses that aren't in First Aid that I have seen on NBME questions, such as female hypoactive sexual desire disorder, but in general psych diagnoses have pretty self explanatory titles.
Behavioral sciences proper is just a crap shoot. I'm going to also try to learn as much as I can from BRS. I mean the NBME in the past has asked questions ranging from what type of health insurance has the lowest out of pocket costs (making you pick between HMO, PPO, HSA, point of service, fee-for-service) to abortions. There are certain rules you can use when answering the "quote" questions, but sometimes it doesn't quite fit the paradigm.