Speaking from Step I, it was fairly on target (best predictor that I had for Step I). For Step II, I am uncertain, but I would guess it would be fairly good.
I felt the NBME tests almost always underpredicted.
If you take NBME and the UWORLD SA, average the score?
Bottom line: I think it is going to depend on the real test. Remember the standard error for a USMLE score can be +/- 6, so even the real test does not produce an exact score so to speak.