Is it possible to permanently brick a Droid X playing around with system files and roms, or will .SBFing always (at least unless you take an electromagnet to the CPU or something) bring you back to factory?
Yeah, it's possible. If you can't complete an SBF, or if your bootloader isn't compatible with the .sbf file. The ways of bricking your phone for good are mainly SBF related. Just make sure everything is compatible and that you have a full charge before SBF'ing anything you your phone.
Oh, and READ. Once you're done reading about any flashing/modding procedure, please, read some more. The more you know, the less chance of messing something up.