The Palm TX will run circles around the NIT in terms of PIM. You will be buying the wrong device if you intend on using it mainly for calendar/contacts. The NIT will run circles around the TX in terms of web access and a few other areas.

I was in your boat, but I recently realized the right thing for me was to get the smallest (and cheapest) smartphone I can (palm or WM) for PIM- that way, it's always handy- and can concentrate on office app and internet experience for my next handheld device (where a bigger screen matters.)

Now I need to decide if 810 is the way to go, or wait a few more months for a (bigger, heavier, more expensive, but probably pocketable) MID device that can run Open Office.

I'm a N800 user (since Jan. 2007) and I _love_ my N800 and won't go anywhere without it, but I still use my good old Palm T3 for calendar and contacts (although I use my N800 for transferring contacts as vcard files - as an intermediary between different devices. Nothing on the N800 is actually using those vcard files.)
And oh, I use my T3 for ToDo-lists as well (mainly shopping lists and the like).

There's nothing native on the NIT which comes close to the Palm Calendar (although the Garnet Datebook in GarnetVM comes close - but then there's the alarms..)