shadi - research cowpaddy (it's included in BT4) and genpmk. The basic idea is to create a hash file of the password list salted with the target ESSID. It takes a little time to create the hash file, but it really speeds up the password search. Instead of using aircrack-ng you use cowpaddy and the hash file to search for the WPA/WPA2 passphrase, i.e.
-r <your capture file from airodump-ng>
cowpaddy -r pwnagetest-02.cap - d pwnage -s pwnage
-d <the hash file you created using genpmk>
-s <the ESSID of your target AP>