Umm.. I think you're talking about the difference of drive size more than the difference of FireWire.
If the drives are the portable ones using the 2.5 inch laptop drives, they consume little enough power to be bus powered by the FireWire bus.
But if the drives are standard 3.5 inch, in an enclosure, they require an additional source of power.
This is true with FireWire 400 and 800.
For FireWire 800 drives without needing an additional power supply, look at CMS external harddrives. The line they have using portable 2.5inch drives require no external power supply. (but remember, laptop drives currently max out at 80GB, and that just came out)