Just an update to this info...
The EMPLANT SCSI was not autobooting for the Amiga side, it was of course for the Mac emulation. The speed was limited by the speed of the Zorro II bus and the device you were using. With fast hard drives we could max out the Zorro II bus width pretty easily.
empscsi.device did work with HDToolBox as well as various caching programs.
I wrote empscsi.device (as well as everything else I did) in assembly, so it was as fast as the Amiga would go.
