It might have been a SCSI drive/controller, but it might have also been that you used FastFileSystem, which was pretty efficient.
One of the HD manufacturers of the time, either Conner or Maxtor, was known to use Amiga 3000 machines to test their SCSI disks, because of the CPU/chipset/OS/FS combination. Not many systems were able to extract 90%+ of theoretical throughput like the A3000 could.