For the record, Topre stemmed keycaps will slip onto a Novatouch slider, but will not snap in. In other words, turn you keyboard upside down, and they fall off. I even attempted it this morning for kicks.
The Novatouch only feels different on bottoming out. They're still Topre made domes, so keypress itself is identical. The springs might not be gold plated, like in the HHKB and Realforce though, can't remember offhand. Shouldn't really matter. And the reason the Novatouch feels different on bottoming out is because of the case. Technically, the sliders will be slightly heavier, due to the MX stem in the middle, but its probably only a gram or so. I can weigh one when I get home.
The sound is completely different, as the acoustics of the case are different. Doesn't sound bad to me with silencing rings installed.
That said, the HHKB is a bit nicer to type on, IMO. The Novatouch isn't bad by any means, I quite enjoy using it, the HHKB is just slightly better. If I could only have one, I'd opt for the HHKB. If I could have two, and wanted two smaller boards, I'd go HHKB and FC600c. Objective as it is, there's my opinion
![Smiley :)](https://cdn.geekhack.org/Smileys/solosmileys/smiley.gif)
Of course, the real answer is to get one of each.
![tongue :p](https://cdn.geekhack.org/Smileys/solosmileys/tongue.gif)