Yet another installation report:
Model Number:CECH-2503B (320GB)
Original Firmware:3.55OFW
Lowest Possible Firmware:3.50OFW
Firmware Installed BEFORE the Firmware Upgrade:3.55CFW KMEAW
Console QA Flag Status:Enabled since the Rollback Brick Fix/Syscon Hash Reset phase/CEX-DEX conversion period -
checked QA Flag status during every firmware change sans the 4.30 update and it was still enabled.Firmware Before Installation:3.55CFW KMEAW (CEX)
Firmware After Installation:4.30CFW RogerO (CEX)
Highest CFW Firmware Used:4.30CFW RogerO (CEX)
Firmware Changes Made on my PS3:3.55CFW KMEAW CEX > 4.30CFW RogerO (CEX)
(via Recovery Mode (MANUAL METHOD)) > Hybrid 4.25 to 3.55 CFW (CEX)
(via XMB) > 3.55CFW RogerO v3.7 (CEX)
(via Recovery Mode (MANUAL METHOD) - prompted me to install "firmware with version 4.40 or later" - but continued anyway) > 3.55CFW KMEAW (CEX)
(via Recovery Mode (MANUAL METHOD)) > 4.30CFW RogerO (CEX)
(via Recovery Mode (MANUAL METHOD) - I've also deleted the ToggleQA, EID RootKey Dumper and MemDump applications now, so I WILL NEED TO REINSTALL TOGGLEQA IF I NEED TO ROLL BACK!) Additional Installation Actions Taken/Additional Notes:- I DIDN'T uninstall multiMAN when prompted as I managed to change firmware versions successfully.
- I DIDN'T install the official 3.55 firmware PUP when some of the more paranoid (can't blame them) users did this.
- I was fortunate enough to have ToggleQA installed since the CEX-DEX conversion phase, so I didn't need to install it again at the time, but now that is not the case, so I WILL need to reinstall it later on.
- I also tested the 3.55 rollback method, and I've managed to do this successfully, although I was told to "install firmware version 4.40 or later" - just press the START+SELECT buttons, hold them down, and continue.
- PLEASE NOTE THAT on the non-KMEAW/official firmware PUPs, YOU WILL NOT get a chance to see the EULA in Recovery Mode, SO MAKE SURE YOU HAVE GOT THE RIGHT FIRMWARE PUP TO HAND BEFORE INSTALLING.
Special thanks go to RogerO, DeanK, The Three Musketeers, Andoma, E3 and everyone else who I forgot to mention for resurrecting the scene from a comatose state! 
Oh, and I'm off to bed now - au revoir!

Source:
http://www.ps3crunch.net/forum/threads/ ... #post57515