If you are Burning certain types of movies files that might have extensive encoding could be a issue of slowing it down
It doesn't have to be how you set up the drives remember some programs can dictate the speed as well check your software if you hardware is working fine like windows says then it would be software related
you said you are using Nero isn't there speed adjustment features ?
I don't think it is how you have it connected
also try another software to see if the speed has changed
More information on your problem this suggest your media disc is the culprit that there not functioning well because of the firmware used take a look maybe you can get a hold on it through this http://answers.yahoo.com/question/in...4121656AAh9FQi