Casio CZ/ VZ/ FZ - Pro Series

Hello.
As you might know, I'm a rather happy owner of the Casio CZ-3000. I 
was thinking of buying a VZ-1, as well, but I'd like to know if I 
really need it - do they sound pretty much he same or can either do 
things that the other can't? How do they do head to head? Any 
suggestions would be very helpful.

Thanks,
Saso.