I am on firmware 4.70 but the exploit https://www.ps3xploit.me/ says it only supports 4.75 to 4.90. Should I just manually update the firmware to 4.90 or is ...
The very first thing you should do before downgrading your console is to create a dump of your flash memory if anything goes wrong during the downgrading ...
Nope you need to downgrade to 3.55 with a flasher and then install the CFW of your choice. There is no jailbreak for anything over that FW. I would not bother ...