DVD-R drives are extremely slow. 24x read, and then even slower CD-R and CD-RW. I would definitely replace the SuperDrive with your LG combo drive, and for burning CDs, you'll really appreicate your LG combo drive. I burned a 700 MB CD in under 60 seconds with your exact same Combo drive. Copying a CD worth of data takes only 2 min or less. And believe me, a 24x CD read speed is not considered fast.
Well, don't forget that the drive's read speed rating is defined as the top speed on the outside edge of a disc. In reality, a CD-ROM/DVD disc reads from inside out, and inside-spindle edge data may only be read at 12 to 15x at the most. If the CD-ROM that you are copying data from is 250MB in total size, then you're only going to be reading data from it at 12 to 15x, and that's pushing it, since the 2MB buffer of the DVR-A04/104 is designed for small file sizes. If you're copying 10 and 100MB files, then the cache won't be helping out much either. Just my 2-cents.
Of course, if you're burning a CD (or a DVD), or copying data off of a CD, why not just start the burning software or the copy and do something else? We do have a preemptive multitasking operating system here?
I've played Quake while burning DVDs and never made a coaster.