The scans look like crap past 3.5GB, but then Pioneers aren't very good drives for PI/PIF testing so I wouldn't take the results with certainty. Do you have access to a Benq or Liteon drive for a better testing drive? Otherwise you can also run a transfer rate test, although there's a fair chance that the TRT will appear perfect, but that still doesn't disprove the error levels being reported above.
Regarding burn speeds, in most situations media will burn best at or near its rated speed. If the burner is poor, firmware support is poor, poor media, etc., you may get better results at slower speeds but T02 should burn fine at 8x. If there is newer firmware for your drive, it would probably be best to update it.
What brand are these discs, BTW?