Hmm...
honestly speaking, I am just too scared to connect and sync my T1 with Sony's software, as I have read some very upset reports, that a whole bunch of books got deleted, because the books were not in Sony's library program, thus it "synced" (=deleted). I even don't have the software installed (it's my work laptop, privately I use Linux).
I found a few threads, which cast some light on your question:
https://www.mobileread.com/forums/sho...d.php?t=156170
https://www.mobileread.com/forums/sho...d.php?t=115827
https://www.mobileread.com/forums/sho...d.php?t=102283
Reading these, I conclude, that exporting notes seems to be better with the T1 than the x50 models.
Besides this I now remeber, that the process of annotating is a bit clunky on the x50. As you plan to annotate a lot, this is one more hint towards the T1, as the workflow simply is better, when it comes to annotating on the device.
Thus, if you go Sony, take the T1. You could order online, play around a bit and if you don't like it, send it back.