You said BetacamSP, uncompressed? If you are doing uncompressed then that ups the stakes. For that I would recommend SCSI or Fiberchanel. I have done some uncompressed with 800Mb Firewire but it isn’t very reliable in my opinion.
If you compress your footage then firewire drives work great. I’ve edited 2 to 1 footage for years on 400Mb firewire drives.
Hope this helps-
Matthew
Quad 2.5 G5
OSX 10.4.X
Ram 4GB
FCP 5.1/AE 6.5/DVDSP4