... the Kawai's can sound very dynamic, but the keys respond that tenacious that fast trills are not really possible, the keys come up too slowly compared to a real action.
I disagree. I own a CA71 and I think the repetition is perfect. Although it's been a while since I last played a grand, I don't see any limitations regarding repetitiveness. And compared to an upright - the keyboard of the digital is far superior to the keyboard of my (Yamaha) upright.
Well, I can only speak about my Kawai MP9500. Of course it should be clear that such a rudimentary key construction cannot substitute a highly elaborated real grand piano action. See only the double escape mechanism - on my grand piano Renner action the keys need to be released only for 2 Millimeters or so and a repetition is possible.
But even if we let aside that missing double escape mechanism the poor piano action surrogate the MP9500 has, it is so that at least on the MP9500 the keys come back much slower than a good grand piano key. A good grand piano action gets a key back with a weight difference of not much more than 20 grams. That means, about 50 grams are needed to press the key down (measured on keytip with pressed sustain pedal), and with 30 grams or more the keys goes up again.
Beside, that some keys on my MP9500 need unbelievable 70 to 90 grams to go down, the difference to go up again is much higher - that means up to 50 gram difference. That is probably the main reason that I have the feeling of pressing almost in foam rubber on the Kawai MP9500, tenacious key feeling it is.