It all depends on how important FM sounds are to you. Do you use experimental electronic sounds a lot, which you edit yourself? Or are samples of natural acoustic instruments more important? In the latter case, I think the advantage of upgrading to the PA-4X and keeping the Motif, for which you can use up to 4 GB of additional flash libraries, is bigger than to buy a Montage.
thank you very much for the thoughts. Yes what you are saying makes a lot of sense.
Comparatively I use more natural sounds than FM sounds. Makes a compelling case for keeping XF and upgrade to PA4X.