Thanks a lot for your response.
I tried as you said, and disabled Powerrec. This helped, in that it stopped the lower plateau rate drops at the end, but the low spikes persist, most every even numbers (8x, 10x, 12x, 14x, and 15x).
I tried Emailing Plextor support, but so far they only Emailed a generic response.
I"ve attached the resultant test (got the same results twice).
Any further suggestions?