Hola , he visto un video y un tema en otra web sobre un downgrade desde 4.0 a 3.55. No se si se pueden poner direcciones asi que si se puede pedidmelo y lo pongo en comentario. El downgrade lo hace asi, os pongo las instrucciones de la web :

Step 1 – Download PS3 downgrade PUP file and place on a USB memory stick in the folders PS3\UPDATE
Step 2 – Switch off power to PS3
Step 3 – Turn on PS3 and keep your finger on the power button though the beeps until it turns off again
Step 4 – Press power button again and hold it until you hear 2 quick beeps together then release button
Step 5 – Playstation 3 will now be in Recovery Mode
Step 6 – Choose update from storage device / usb and let PS3 update
Step 7 – You will be prompted when it is finished to insert usb with required firmware on
Step 8 – Copy the PS3UPDAT.PUP file for the jailbreak firmware you want (ie 3.41, 3.50, 3.55) to the PS3\UPDATE folder of your USB
Step 9 – Choose update now... wait... and your downgraded!!!

Tranquilos, si lo marcais como fake solo destrozareis mi corazón.