I don't think a DVD burner itself will ever require more processor than you have. The highest burning speed we are ever likely to see is 16x, if we even see that. And your processor shouldn't have any trouble keeping up with a 16x data rate, as long as you have DMA enabled.
Now, you might someday want a faster processor if you do a lot of transcoding of mpeg files, since that can be pretty processor intensive. But you would do that ahead of time, not while burning, so it wouldn't affect your use of the burner itself. Unless... what about simultaneous on-the-fly ripping, transcoding and burning, all at 16x???
I don't think so.
cfitz