The error pattern at the end of the disc on the first drive is in the low-solid-block pattern indicating a mild communication interference. Scanning at higher speeds is necessary to determine if greater errors are actually present on the disc.
Ah, scan the all of the output/test discs (from both drives) in just one drive (the second drive).
We can't compare written output that is SO close without a common point of reference (write discs with both, but scan with just one drive).
Also, try the latest cd/dvd speed from cdspeed2000.com and manually set the scan speed to 12x as this [is the burn speed used and] will magnify the differences.
Next repeat the test using the first drive to scan all of the output/test discs. Use the same cable--do not switch cables or ports--switch only the drives.