Update: Today, I pulled the trigger on a very lightly used (home only) Tyros 4 and speaker system for £1,500. Picking her up Monday.
In the end, I decided I just couldn't justify spending twice the money on something which is only going to play a secondary role in my work pattern (at least for now). Having watched lots of Tyros 4 videos, I concluded that there was plenty of inspiration in the T4 to keep me busy for some time. It also means I can afford to keep the Kurzweil, which is a very capable and convenient board to have.
Once again, thanks for all your input. I'll tell you if I made the right call in a few days!
Congratulations on the Tyros4.
I still love mine. It is an amazing board and can keep up with the PA4X and T5 when tweaked correctly.
You can really get great results with the octave up and down button to ad 2 octaves to your keys.
You can even assign this function to foot pedals.
Have fun exploring. There is a lot of potential in that machine
Eric