the only thing i've heard in this regard is that the verbal score is highly correlated with passing step I.
I just found these excerpts from MCAT research articles:
"Prediction of performance on the USMLE examinations, including whatever variation is induced by methodological factors, is a valid and important role of the MCAT."
-- <a href="http://www.aamc.org/students/mcat/research/bibliography/julia001.pdf" target="_blank">http://www.aamc.org/students/mcat/research/bibliography/julia001.pdf</a>
"As expected from many earlier studies, MCAT scores were consistently more valuable that were undergraduate GPAs as predictors of performance on licensing examinations, supporting their continued use in selection decisions. These relationships are stable across three decades and apply to the three examinations. Verbal scores tended to be better indicators of performances in the clinical and postgraduate tests."
-- <a href="http://www.aamc.org/students/mcat/research/bibliography/velos001.htm" target="_blank">http://www.aamc.org/students/mcat/research/bibliography/velos001.htm</a>
Both articles found here: <a href="http://www.aamc.org/students/mcat/research/bibliography/start.htm" target="_blank">Annotated Bibliography of MCAT Research</a>
If you have a low MCAT score, that doesn't necessarily mean you'll do poorly on the USMLE exams. Just study hard in med school!