Keeping that in mind:

• IDE drives can use ATA buses slower than that which they are rated for very easily.
• ATA buses do not like IDE drives which are slower than the bus rating, as it makes the controller work harder.
• Booting from the ATA-66 chain or an ATA-66/33 drive on the -100 speed bus is not recommended and not officially supported by Apple in the MDD macs.

Generally speaking, it is always better to clone an existing volume to a new drive than to simply keep moving an older drive from one machine to the next. By cloning, you get the opportunity to change your partition scheme, increase overall storage availability on the boot drive and get the added benefit of switching to a low-hour drive.

I used to drag old hard drives to new machines, until it royally screwed up my MDD dual 867. Since then, using firewire target mode and a cloner has made life much much easier and simplified my partition scheme without the need to restore from a backup.