Zachzi, what firmware are you using? BenQ should really improve both DL and RW burn quality and reliability. I wonder if these issues were addressed in the new BCFC firmware.
I had 4 DL coasters (Verbatim MKM001) with my first defective DW1650. Haven't burned any DL media with my new drive yet, kinda reluctant after that costly incident. For now, I let my good old (and trusty) NEC 3500AG do the DL burns.