EDIT: Oh looks like my thread got stickied. Well I'mma add a bit more info in here for anyone just stumbling in then.
Looks like we got a leak. Daywalker posted a .621 SBF file at XDA. (Ironic, thought the XDA Droid X forums were pretty dead)
[SBF and Update] Original Gingergread 2.3.4 SBF for Droid X MB810 Verizon USA - xda-developers
Still can't revert to earlier firmware. If you are on .621, you will remain on .621, and a root exploit is still not found for .621. But it looks like we have a way to revive a bricked .621.
If you need a link to the .621 SBF file I am hosting it in my Dropbox. All props go to Daywalker at XDA for the leak, Dropbox is just a heck of a lot simpler and faster download than the original mirror. You can find my hosting links for this SBF @Rootz along with MD5 checksum info, below. To flash you will need RSD Lite 5.4.4 and of course the Moto Drivers for your PC: