Reply to S4 vs. Vci-400 ?

I believeing about upgrading my setup.
I've been using a VCI-100 SE for a while, and been quite happy with it, but the 4-deck possibilities in the VCI-400 and S4 seems alluring to me.

So I'm turning to you, my fellow travelers in the world of digital DJ'ing, for advice, pro's and con's of the VCI-400 and the NI S4 - which one to buy and which one to leave on the shelf ?

Thanks in advance