@Sandman
In combination with a fast CF card, The CF-IDE should give you at least 7 MB/s. I can confirm what ddniUK already said. If I set my cyberscsi to asynchronous mode, it halves the speed. In synchronous mode I get ~7.5 MB/s.
This is with a scsi-ide adpter and CF-IDE adapter with a Sandisk Ultra II 4 GB CF card connected to my Cyberscsi, which is a Fast SCSI 2 controller.