The firmware changes for one Kindle usually get ported over to the other recent devices.
Amazon doesn't just do radical changes to the device firmware.
I believe there are a few more fonts available on the PW, my KT only has three (Caecilia, Caecilia Condensed, Helvetica) and simply never got updated, but I had to look that up as I never changed it, like, ever.
Any differences are likely to be minor.