The "PI Errors" represent all of the errors as they are read off the disc. In your example, there are over one million PIE's, and they peak to 564 which is a lot (I like the total to be under 100,000 and the peak below 100). Fortunately, a DVD disc is written with two separate levels of error-correction data. The first level of error-correction data is applied against the PIE's and it will attempt to correct all of the errors.
Unfortunately, DVD pits are so small, that this "first level of defense" error-correction data will not be 100% successful in fixing everything, although it can get REALLY close (say under 50), with premium discs. Errors that are NOT corrected are called "PI Failures" because the first line error-correction logic FAILED to correct them.
These PIF's represent ALL of the remaining errors. At this point, the PIE's have become irrelevant, since the first line error-correction logic has already been applied against them. In your case, the 1,000,000+ PIE's have been reduced to a mere 2,089 PIF's peaking to a maximum value of 10. This is VERY GOOD because it means that nearly all of those PIE's were VERY correctable.
The "second line of defense" error-correction data is, in turn, applied against the PIF's. Since this represents your "last chance", it must be 100% successful. If it's not, then you will get the dreaded "PO Failures" box counting up errors. PO Failures should always stay at a count of zero, or you likely have a coaster.
CDSpeed produces a quality score based totally on the max value of the PIF's. In your case, this peaked to 10 somewhere near the middle of the burn. A peak of 10 will always give a quality score of 94%.
Hope this helps!
Edit: One last thing - your scan looks a bit strange. The speed keeps dipping down on a recurring basis. This is normal for higher speed scans - both 12X and 16X will do this. But it does NOT normally happen for a maximum (8X) scan. You might try to close down all applications, remove any disc from the burner, and repeat your B7T9 flash.