These tests are just too different for there to be a very direct correlation. Granted, I'll agree that those who score high on the SAT will, on average, score higher on the MCAT and other standardized tests. But if you look at the SAT, what is it other than a glorified vocabulary exam? The MCAT requires 100 times more preparation than the SAT ever did, and therein lies the problem. The amount of preparation varies greatly from one person to the next. IMO, two tests that that would have a much better correlation would be the SAT and the GRE. I dunno how many of you have taken the GRE, but I took it last December, just in case I don't get in this year, and my scores were eerily similar to my SAT scores.
SAT: 760V/740M
GRE: 770V/740M/770A
They're pretty much the exact same test, except that the GRE is computerized, and you have to go straight through on all the sections, which kinda sucks. No coming back to the tough questions you don't know. Oh yeah, the GRE also has an analytical section to mess with your head and make you solve stupid little puzzles.