I think they are billing the Joystick more as a freestyle board but IMO it is (or was, the last time I rode it which was last Feb) really an all-mountain board. I actually prefer that one to the Custom FV for all-mountain riding. Actually, I don't like the CFV at all really. But the Joystick is a really fun board.
I recently bought a Sherlock for pow (which I rarely see except for trips out West) and the occasional groomer days. It's definitely on the softer side of "all mountain" but I'm loving it so far for those days that I'm not spending any time in the park.
Flex-wise Burton says the Joystick (4) is softer than the Sherlock (5). Perhaps I don't remember the Joystick as much as I thought, but I didn't get that soft of a ride out of it.