I would leave the 48x CD-burner especially if you want to keep burning CD's as well. You really will not find a DVD-burner that will adequately match the burning speed and quality that a standalone CD burner would give you.
Just as with any burner the more you use it for reading and writing the greater the probability that you will wear out the drive. These quality DVD burners are dirt cheap now and can be easily be replaced with a newer/faster drive for the same cost if you have to replace the drive.
A DVD burner was meant to just be used to burn DVD's and a CD-burner to burn CD's.....so just keep that in mind.
I have a BENQ1620pro B7T9 and Lite-ON 52x CD-burner. I really don't want a DVD-ROM by itself since I never watch a movie on a small 17" screen.
Most systems today come with a DVD/CD-burner and DVD-ROM which I really don't like.....why...The DVD/CD burner is working overtime for both media which puts extra stress on the unit and will increase the unit will die compared to stand-alone units.