Well I finally got to play a CP4 myself today. I had already recommended it to 2 students solely based on the comments in this thread. I went over to one of my student's houses to try his new instrument. I took my EV ZLX12P to hear how it would sound through the rig I'd be playing it through. I also brought my headphones.
Based on everything I've ready in this thread (18 pages for me) I had high expectations. I am really happy to say that this instrument exceeded them in every way.
Action: Very solid and extremely playable. Based on what some people were saying in this thread I was worried that it might be too 'heavy' of an action. I don't know what they meant, but the action was extremely pianistic and I was very pleased with it. I'll have no problem playing quickly and easily on this beast live.
Piano Sound: I am so thrilled with the brightness of the new sample. This will likely be my go to for live stuff. Bright enough to cut, but substantive enough to stand on its own. Sounded awesome and FFF and PPP.
Other Sounds: Rhodes were very inspiring for me. I am not a Rhodes aficionado, but I think I have everything I need. I was really pleased with the dynamic response as well from a whisper to a banging FFF. I was also very happy with 2 other inclusions. I am thrilled with the amount of synth sounds included. They aren't really editable, but they will be very useful I think when I couple this board with my XS6 for Top 40 playing. The second thing that blew me away was the HARPSICHORD. I stumbled upon and was floored with how great it sounded and the awesome release samples. I couldn't help but play all the Bach I had memorized. I wish I had brought some more to play because it was a real joy.
I was impressed with the evenness of the sound and response throughout all registers. Jazz lines sounded great through the whole range of the instrument.
Lastly, I was really impressed by the simplicity of the layout. It was so easy to do everything I wanted to do. Setting up a split was a cinch, and even routing reverb to different parts of the split was so natural. They really make the most of that little display.
In short, I will be buying one ASAP. I think Yamaha has a huge winner here, and I would expect this to become a benchmark for years to come. Great job Yamaha.