As others have said you need a good quality controller, ideally PCI-e, to take advantage of the speed such scsi drives offer. Not worth the price increase over SATA IMO.
Thats where i got my scsi card in my sig from bout 80 quid, still need to set it up properly tho.
Dont know real world figures performance wise compared to raptors or u320scsi but the new serial attached scsi (SAS) drives have the max theoretical transfer speeds. (Think its 600mbs)