I don't think getting hold of the iCloud password would let anyone "own" my mac. (The only things they should be able to do with that would be messing with my synced address book, notes and photostream - and if "find my mac" was enabled, perform a remote wipe).

Use FileVault 2 and remote wipe is no longer necessary.

On current Macs, a live USB stick might be a better idea than a live CD. Or even better a bootable backup created with Carbon Copy Cloner (CCC) or SuperDuper.