I can give you a 27megs/sec reason to get an acard scsi to sata adapter. Works great with the CS MKIII.
The IDE will be much slower and much more cpu intensive...
I keep thinking I would like to grab one, but I also have a CS-MKIII. 68-pin SCSI to SATA adapters are not cheap, especially ones that support hard drives. I have one for IDE for my DVD-RW, but it only supports ATAPI devices.
I could buy the FastIDE and use an IDE-to-SATA adapter (or one of my IDE SSDs,) or I could find a 68-pin SCSI-to-SATA.
Decisions decisions.