20 Hex values? Someone with math can correct me, but isn't that 20 to the power of 256, or 20 with 256 0's afterwards? I'm not sure you'd crack that anytime this century.
Oh, and there's a hitch, at least with my HD. If you run atapwd, it shows you a few atributes of the HD you're working with. After 5 attempts to unlock the HD with a password, it hits a limit until the drive is power cycled. The you can try 5 more... reboot... lather... rinse... repeat.
It's not getting cracked with a brute force attack, that's for sure.