Thanks for the feedback.
The motivation to try the Firewire cable is for the faster transfer speed. The thought was that maybe the external device could be plugged into the same computer with two different ports, and default to the fastest one.
BTW, I don't see an obvious way to stop the cloning process. Well, I guess I could Force Quite CCC, unmount the drive and see if it mounts with a 6-pin Firewire cable. For now I will just let it slowly transfer the data through the USB cable.
thanks again, and wishes for a happy and a merry to all
Todd's keyboard