Okay when I say no correlation I don't mean like literally zero but what i'm saying is that its unpredictable. Here's why. There are so many topics on the MCAT and each Khan passage only covers one topic. In addition each passage only has five questions, whereas a normal C/P passage can be even longer (up to 7). In addition you cannot go back and forth between questions before submitting answers unlike the real thing. The formatting is not like the real thing so that's why I say it is not predictive. You can't just keep track of how many you got right and then correlate it to success on the real thing.
What I do think is correlated to success on the real thing is doing khan passages. The more you do, the higher your score improves. Personally I was always pretty good at C/P type stuff (i'm a math person) but the bio section was killing me on practice tests. I ended up doing over 100 khan bio passages and went from average bio scores on practice tests (I once got 54% correct on an ek exam and a 123 on a tpr exam) to getting a 130 on the bio section on the real thing. So don't worry about how many you get right in khan, worry about how many you do, and how much in detail you go over your mistakes. Does that answer your question?