Going back to your original post at the top, you said you might try the PfD or a different rom, I can't speak about putting another rom on the 925 as I've never done it but was in the PfD at one time, but as xandros9 states, technically the PfD does not deliver Denim.
I'd start chasing the windows phone team on twitter or similar and also nag ATT to get their finger out and release the Denim update, this is making the assumption that the Denim update does include that fix, that is what I would be chasing the windows phone team about, is that fix included in Denim? Pointing them to that thread on Windows Central, or that source URL at answers.microsoft.
Waiting for WM10 could take an age, I don't expect to see that until the first half of next year, brand new ones with it on in maybe September or October but the rest being updated slowly.
I feel for you, my brother was gutted as he loved his 925 and would probably still have it today if it wasn't for that locking up issue, back then we hadn't got a clue what it was, trying all kinds of things to get rid of it, the only thing that worked was rolling back to 8.0, but eventually we lost the ability to do that as the NSRT at the time stopped offering that rom and started pushing 8.1 with Cyan.
Actually, that is a good point, if you don't mind flashing roms and you can get your hands on the ATT 8.0 rom I am almost certain that would work for you. Not ideal but the freezing would surely disappear. No notification centre though, no 3 columns of tiles, older version of IE plus other things you would miss out on but the basic phone would still be the 925.
Good luck and keep us posted,
J.
EDIT: While I was having my own personal nightmare the other day with WM10 and rolling back out to WP8.1 I stumbled across a thread where a user had this locking up issue fixed by updating to Denim, the link below points to the last page and the user xma1e_ stating that his issue was fixed in January by MS when Denim rolled out. Going back to page 1 you can see that his issue is largely the same as yours and my brothers. His is a Lumia 1020 though, however the locking up issue is widespread across 1020s and 925s.
http://community.o2.co.uk/t5/Other-Devices-Nokia-Blackberry/Nokia-Lumia-1020-Random-Freezing-since-WP8-1-upgrade/td-p/715511/page/3