well then you need to try this as it does work from another user has already tested it and left a comment saying it works for 3000x models. if your talking about 4000x model super slim i doubt a boot loader will change if you can still read or write to its own nor when its the exact same brand as any other slim that the e3 fits on.
and if your saying it doesn't work trying to go to 3.55, in this case here this does not go to 3.55 at all, its on a firmware that 3000x models have been on and are able to downgrade to.
i'm guess i'll make another video on a 3000x console, CECH-3001a to be specific specific to prove this works on 2000-3000 slims models. only thing i can say is i don't know if it will on 4000 since i don't have one.
dont try and dig yourself out of a hole here, sony changed the bootloader keys on newer consoles also 3000x series has metldr.2 the newer ps3's are very secure because sony fixed the sign fail bug that the fail0verflow team found which stops us calculating new private keys also they removed linux support. so you would need the new private key then you could sign loaders on the newer console then install linux and see if you can exploit the new bootloader. but it aint going to happen