If you have awesome test taking skills you'll have an easier time on both thats for sure.
In general, people who work hard in high school work hard in college, work hard in med school, and will work hard as physicians. In general, people who are of above average intellect in high school will remain of above average intellect in college, of above average intellect in med school, and of above average intellect as physicians. Since scores on the SAT, the MCAT, the USMLE, and really whatever else standardized test you're taking about correlate well with hard work and intellect, scores on one standardized test correlate will with results on later standardized tests.
As pointed out though, the group you are competing with does get better with progression, and you will tend to have a dropping percentile trend as you advance in the exam hierarchy. 99th percentile SAT probably equates to about 95th percentile MCAT and probably around 90th percentile Step 1 due to the constant weed-out that occurs along the way. This is, on average, of course. Some people jerk off in high school or college, or become more inspired or decide to coast on past achievements, or whatever. But, in general, yes, the exams correlate.
In terms of your specific question, I wouldn't try to apply this general trend to your individual case. Work hard in college, do well in the science courses, and you'll do well on the MCAT.
