Optical drives always surrender control of the bus to the drive in the Master position. If that drive has a slower controller, it has the potential to monkey up burns. This is true for both CD and DVD drives. Because of the higher transfer rate of a DVD burn (even at 1X it is 9X for a CD) it is crucial to ensure the burner can sustain the highest data rate possible. That is why it is best to set a DVD burner to Master. It is equally important to not have a drive in the Slave postion that will be accessed during the burning process. If that drive has a slower interface, the Master drive will notch down the speed of the channel to match that drive's lower speed. Also if that drive or the controller itself does not support or have Bus Mastering and/or DMA enabled, it may cause sags in the data stream as well. Thus, if another drive must share this channel, they both should be using the same transfer modes--preferrably UDMA on a Bus Mastering controller.
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.