Well I've just 'risked a coaster' and burnt a Fujifilm YUDENT00 T02 that Qscan said wasn't worthy of being burnt at either 12x or 16x.
But I burnt it at 16x by accident (forgetting to change the speed in nero cd-dvd speed options).
Looks like Qscan was right.
Thing is the dvd is still playable, the Quality score stayed at 97% until the very end. I'll be keeping this 'coaster' i think.