I can tell you why I would agree with jqp, EchiDna.
I have both a Plextor Cd burner and and Plextor DVD burner. CD unit much faster dealing with CD formats, than DVD unit. Even just reading directories of CDs I've burnt. My guess (at least per my situation) is that the DVD unit can recognize more formats and takes its sweet time figuring out what it is looking at.
If I am scanning thru a bunch of file disks I've burnt on my machine, I always look thru the CD unit. When searching CD directory, machine speed sucks until it comes up with something. Nature of the beast. I previously had just a DVD play unit along with the CD burner, and it was the same way, real slow at deciding what it was looking at.
Regards,
DeadFish