
  Your source is wrong.  The double speed CD300 is still slow compared to a
typical hard disk.  The LC can easily handle the SCSI transfer rate of the
CD300.  None of the current Macs, even the Quadras, support SCSI-2 unless
you get a SCSI-2 Nubus Card.

  You don't have to have double speed to use PhotoCD.  It's just faster
reading images off of a disk.  I think that the CD150 can handle PhotoCD,
but only single session.  The CD300 can do multisession PhotoCD.