Drive manufacturers test media and program their own burn speeds for various media into the drive's firmware. They will generally allow burning up to a speed that is just shy of coastering the disc. This in no way indicates what the drive manufacturer found to be the best speed. There is considerable evidence that burning at rated speed or only slightly higher will produce the best quality burns with BD-R. See here.
Thank you for confirming what I was very much hoping for :). Nice to see another company got smart and started sourcing their BD-Rs from FTI. I'm glad you decided to grab those Digistors. I've been waiting to hear from someone in the US confirming the change over here. The 6x Digistors I tested a few months ago were CMCMAG-BA5 discs. Not the greatest burn quality.
Here is a screenshot of an Imgburn graph opened in ODC. You can save it as a png file with the floppy disc button. I find it simplest to name the graphs with "%B %M %I %S %V" and keep them in a custom folder like "my documents/Imgburn Graphs" for ease of access. You can also access them from ImgBurn>Help>ImgBurn graph data...
If ODC 1.70 does not cooperate with opening the files, Download 1.50 and install it in a separate folder from ODC1.70.