Firstly, 16x is the maximum read capability of the drive, but only under ideal conditions with defined media. Practically you will only get near 12x as you approach the outer edge of the disc (if the drive reads at a constant rotational speed). You also have to remember that many commercial pressed DVDs are double layer, the reading of which tends to be slower than single layer.
By the way, I see you have a similar thread (here) over on the LiteOn burners forum, where a firmware and Omnipatcher have actually been suggested to allow you to set the drive read speed. It would help if you tried that next and reported back there with your findings, because at least one other member has the same drive.