My point is that you can't draw conclusions about two different people this way. If playing speed metal is a good mental exercise, then the only thing you can conclude about Dave Mustaine is that he's smarter now than when he started playing. You can't conclude that he's smarter than anyone else, no matter what activities they participate in. The classical musician very well may have started out at such a high IQ that no amount of mental exercise will allow Dave to catch up.
