The disc should be perfectly fine. The Optiarc can successfully read the disc; just about every other drive can get past those yellow “damaged” sectors you get when you run PI/PO scanning. All that does is tell you that the error correction of the drive is being applied for that part of the disc. All discs will have a bit of yellow if you use PI/PO scanning–and possibly might have a bit of red–and still be of more than acceptable quality.
Now, about the gray areas. My guess is that either the drive or DiscSpeed dropped samples while scanning the disc. This doesn’t necessarily mean that your data isn’t there; it just means that, during the process, the drive or the software “skipped” over reporting “quality data” for that part of the disc. It is probably green, though.
I have attached a screenshot of a scan, and you’ll note that there is a big block of gray at the beginning–before & in between the black. The disc is still flawlessly read, however, and I have no concerns about its quality. The gray comes from the fact that the drive was spinning up to its full speed and, thus, wasn’t reporting any data for that part of the disc.
The important thing is that the drive was able to complete the Transfer Rate Test successfully, and it did the READ TEST for the ScanDisc in all green. That means your data is there, and can be read back perfectly fine. And doing the PI/PO test for the ScanDisc tab is, to me, less informative than just doing a Disc Quality scan [though they report the same thing, just in different ways].