So, I've just finished to restore my backup (got all my settings back) and repeat the whole procedure:
- Updated the system
- Downloaded and activated kernel sources and devx SFS files
- Compiled and installed the Nvidia proprietary driver (with the --no-opengl-files option)
- Downloaded and activated the new Nvidia SFS file
- Updated the init script with the version provided above
I'm happy to confirm that everything works fine now: no problems at all! Both the desktop and the laptop boot flawlessly and I have 3D acceleration on both PCs. The desktop boots with the Nvidia proprietary driver, as expected, since the nouveau driver gets automatically blacklisted.