I am an owner of a standard C3X. While shopping I seriously considered buying a C3-Silent and tried one out extensively. My observations were that the action of the silent CX series is exactly the same when the silent mechanism is engage and dis-engaged. The silent mechanism does not change the feel or touch of a silent piano compared to itself in silent or acoustic modes. However, the action regulation is actually slightly different from a standard C3.
The silent and Disklavier CX action regulation have been adjusted in order to accommodate the optical sensors and silent mechanism bar, and this slight difference in regulation of the action means it is harder to play ppp (with silent mode on or off). Try this the next time you're at the store. Try playing ppp at a standard CX and a CX-SH (preferably same size and model otherwise) without engaging the silent mode. You'll find that the silent model's regulation is different especially noticeable when playing softly. Otherwise, at all other dynamics, it's not noticeably different. Whether this is deal breaker for you is hard to say.
It all depends on your playing style and your skills in adapting to the action and whether the silent feature is a high priority. By the way, the better your skills, the less this would matter. For a concert level pianist, the difference is probably not worth mentioning. I have done some homework including asking a concert pianist (http://lisayui.com/
) who owns such a piano whether it makes much difference and she told me it does not. The difficulty in playing ppp on the SH may well be something that someone like myself who is less skilled have more trouble with.
I have to say that the binaural recording in the SH feature is so well done that I've heard many forget they were wearing headphone and often stood up and started walking away from the piano with the headphones still on and plugged into the piano.
If you decide to purchase one, make sure your tech knows the different specs for action regulation of a CX-SH versus standard. Also, there's a cable that needs to be unplugged from the action first before removing it completely for voicing and adjusting the hammers.
Hope this helps.