Nero Burning Rom never limits write speed for DVD writers as far as I have tested myself. It's the same 16x max speed for MCC004. Same 12x for YUDEN000T02 and RICOHJPNR02. If you are experiencing 6x for the media otherwise should have shown 12x, it's not because it's trial version of Nero but because the disk has dirty or scratched surface or the HDD is too much fragmented or the PC has a wrong driver installed or there are some background processes running at the same time that draw most of the available CPU power or something else. Too many possible reasons and that is why I recommend trying DVD+RW media if you do not have a very good guess at why.
I do not and cannot recommend replacement of the drive to a person who has just bought a recently released product. There have been too many people in South Korea who return Lite-On drives. The most important Lite-On service center in South Korea closed the main office in Seoul very recently because they were losing too much money from their ODD business. Since that, I have to go to their HQ office in Bundang instead of the former office in Seoul which was about one hour closer from my home by subway. Most of the returned drives are returned because the customers just want new drives. The generous replacement policy of LG and Lite-On in South Korea DO account for a lot percentage of their retail prices. The retail prices are about 30-50% higher than OEM prices. Guess how much they spend on distribution channels and drive replacements.