I'm guessing this is a firewire external you are building. Unless you have a Quicksilver G4 or later, you won't notice the speed of the Oxford-911 chipset for the firewire bridge, get a cheaper external case that doesn't have the Oxford-911 chipset.
If you have a QS or later G4, get the Oxford-911 case, and the WesternDigital 8meg cache drive, I'm running 2 80 gig models, and they SCREAM. You can find them rather cheap too, (do a search on Pricewatch for Special Edition) I paid $106 after shipping each.