It is the best predictor of your score. However, it also depends the version of the test you get on test day. I know for BIO and PAT my scores were pretty similar for the actual DAT, but everything else varied. Especially my OC and GC. I got a 17 on OC in 09 and a 23 on actual, and I got a 21 on GC in 09 and an 18 on actual. So it all depends.