I have some very bad writing results using Sony 8x DVD-R. I have my results posted in the thread about the DRU-710a Review done by Ian here in CDRLabs.
Right after I updated to BYX2 they pulled it from the US website although it was still available in Europe and Australia. I spoke to a someone at Sony that was very helpful after getting a few clueless front line pat answers and they told me they had a few problems (?) and it would be better if I went back to BY02 and do not use Sony media
I think your drive is the same except in the external case so the same rules probably apply.
I did switch to Verbatim 8x media and it is working very well with the BY02. I am considering changing back to BYX2 wondering it the original media I used was at least part of the problem.