I have some Sony D21, I will burn one at 8x soon, so that we can get a full spectrum of speeds.
If you can, please find an MCC 004 disk, so that we can see a scan of a burn at 16x or more with it: my external case won’t go over 17,5 MB/s during burns, so 16X is not possible (but 12X is already ok for me).
Some tips: please also save the images as PNG, not JPG, to get a better quality with this kind of images, and put the info about the burn and the disk in the post (to help people find these posts with the forum search), just as I did: brand and disk code, burn speed, scan speed, remarks/notes.
Moreover, could you write the scanning ECC interval that CDSpeed gives you at the end, in the bottom of the summary?
Both my scans were done at 8X and I got about 5,3 ECC. By using 4X and an internal drive you may be able to get better (lower) values: the drive tests more often the sector of the disk.