I have recently purchaced a N5ex and so far I am very impresed. The extra 6MB of ROM makes the N5ex a N1 with a N5 look. The multi mode is very good (I use it with Cubase VST on a mac) the arpegiator is average and is probably more of a sales gimic!
The real time controlers are a nice addition adding a analouge LIKE function. However the canges in Cutoff/Freq are not to smooth.
Over all I highly recomend this keyboard!