First, i think that you shouldn't neglect pat and qr, and unless you're naturally good at them, the achiever will not be enough practice. Id recommend crackthepat, and any qr book you can find (i used an examcrackers mcat verbal reasoning book)
Second, I dont think i would consider the destroyer as a "back-up resource" I thought it was fundamental to my studying. But i agree that you should have other resources on hand-to fully understand every answer in the destroyer, and especially in the bio section you need to have either a very thorough knowledge of biology or at least another media (i used my old text book and schaums, i know other ppl use wikipedia,etc.) to use. But if you know the destroyer cold, you should be well prepared for the dat.
AA 22
TS 22