Hi there - first post :-) I was a member of the old Mad Max Casio forum from the mid-2000s which was gone a while ago, so was looking for a new place to post. I'm sure there is a Casio group on Facebook, but I prefer forums to social media.
I have owned a CTK601 in 1997 then I switched over to a WK3500 in 2005. What I liked about the CTK601 was that you could layer 2 voices together in synthesiser mode, then re-package it as a single custom voice. This was a feature that the WK3500 didn't have, but the WK was better keyboard in pretty much every other aspect. I loved the DSP button. Also, the WK was better for saving your work. For the CTK, you needed an external data MIDI filer which saved your work onto floppies. The WK had an internal floppy drive plus a Compact Flash drive which was what I ended up using.
Then around 2013 time, I moved over to a Yamaha PSR E423. The arpeggiator was probably its best feature for me but I preferred the Casio sounds. So I was like to go back to perhaps either a CTK7200 or a WK7600. Which do you think would be the better option for me? I mainly write dance (house-type) music, so would like a keyboard where you can make your own rhythms. I remember that the WK3500 allowed you import rhythms from the net, but I would also like to try my hand at making them myself too.