I would have tried to go SCSI on my new computer

I did -- I got an Adaptec 19160 card and a 9.1Gb IBM SCSI 10Krpm disk. I've not regretted it (touch wood). This was a while ago. If I had to do it again, I'd buy a 36Gb 15Krpm disk.

That said, my scanner's USB (bus powered). It's a Canon N650U.
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-- roger