I have the same exact problem with my recent purchased SONY16D1.
I used to burn them perfectly at 4x (burned over 200!) and then get a perfect curve on Neros Transfer Rate Test.
Now, I bought a new pack with 50, and I cant get a good Transfer Rate Test if I burn them at 4x, but get a perfect test if I burn at 8x!
How come?? Are these fakes??
My burner is an LG 4163B A105.