Hi Ian-
First of all, I'm no expert by any means, but I had an X3 for a couple of years and truly loved it. The N264 seems like the logical way to go if you ask me since it's very similar to the X series but with more sounds and a few nice features added.
If I were you, I'd do all of my sequencing on a computer and forget trying to use any on-board setup. Words can't describe how much easier it is.