If you choose to update to a custom firmware, you're free to go back to 1.5 via the recovery menu.
Oh, 3.40 OE-A and 3.30 OE-A' are the newest firmwares (3.30 uses an older version of POPS (PSX emu) which uses the same save format as all prior CFW) and, well, with custom firmware, you have the features Sony added in the official firmware, the homebrew they blocked and the ability to run backups. *cough*
Bookmarks