Wow! 5 pages for what you would think was a simple question!
FWIW, I had no problems going from 9.1 to the 'new' 9.0 within 10minutes, doing a simple backup and restore. ymmv, but these were my steps.
From 9.1:
1. Remove the beta profile
2. Backup to iTunes and then archive the backup under preferences>device.
3. DFU
4. Plugin and restore with the latest version of iTunes, which will automatically load 9.0
5. Restore from your backup (there should only be one now listed with the latest version of iTunes)
Restore conpleted in about 15minutes