I'd use B7T9 and burn them at 8x. I've found this media gets a little on the flakey side when jumping up to 12x even on the NEC ND3500AG and while they are still "good" burns you get much better quality at 8x for the difference of a minute or two of time which will probably help the longevity of the disc. I'd rather go at a slower / steadier pace and get a nice result then a faster pace and take a potential to ruin a disc.
I look at it this way now - if I can burn a disc at 8x in 9-10 minutes then I'm happy. It's still a tad faster than 4x and I feel like there is actually a purpose to owning 16x drives, hehe.