With the official fw it burns at the rated speed of the media. If you want to burn at over the rated speed of the media, you have to use >NIL: 's hacked firmware. Then you can burn 4x mdia at 8x and 2 x media at 4x. Of course if the media is not very good, then you won't get good results. I think with the medias that you have, it should not be a problem.