Burn the full disc to get the true response of your media. Most problems occur at the outer edge due to manufacturing problems of the media, not drive response.
The test will give you a summary at the end of the test showing PI, POF and average. The graph charts the location of the errors and shows a limit line of 280. If your media exceeds that, try a lower speed. It most likely is poor media response. If a lower speed is still bad, then the drive is questionable. Just because media can be written to 12x doesn't mean it should be. Verbatim 8x was known to be crappy about mid year. The revised 8x media has a "12x" compatible legend on the disc. If yours does not, try and stay with 8x or lower,