Upgrading PS3 Slim Hard Disk with cfw

I have a PS3 Slim with 250GB hard disk. I want to upgrade to a 500GB hard disk, but am sightly confused in regards to the firmware. Some say put the official firmware back but some don't mention this. At the moment the system has Rebug REX.

My course of action is to take existing 250GB hard disk out, replace with 1TB hard disk, Restore PS3 System and when prompted for firmware I put in usb stick with the following:

USB Stick/PS3/UPDATE/PS3UPDAT.PUP (Rebug REX renamed as PS3UPDAT.PUP)

I...

Upgrading PS3 Slim Hard Disk with cfw