So here's a quality scan of the same disc as the above post, scanned on winxp on an internal PATA Benq 1640. It's basically the same result as the PATA Benq 1620 attached via an external HD enclosure on my linux box. Pretty neat - this 1620 was just sitting in my spare parts pile, it looks like I could use this as my "quality scanner" since it's giving the same scan result as my beloved 1640.

I still want to try the PATA 1640 on the external enclosure on the linux box to compare to the 1620. Maybe that transfer test will work right....