I'm not sure what you mean when you say the RM2 has "pretty much none" when it comes to PDF reading and annotation capabilities. That's pretty much exclusively what I use my RM1 device for and it works great.
EDIT: Wow. Looked at the A5X and for the price compared to the RM2, it's very enticing. (Once you throw in the folio and the pen for the RM2, the A5X is comparable if not cheaper.) Since my old Kindle Keyboard died a while back, I haven't replaced it. Looks like the A5X can also read Kindle books which is a huge draw for me. Do you know if there's any API that allows me to write my own utilities to sync with the A5X? Specifically, I want to be able to send PDFs to the device programmatically that will be eventually synced the next time I use it.