Interesting problem - could be a few things.
1.) The connection between the external writer and the laptop. Most writers require USB2 or Firewire because of the speeds and size of data involved. Do you have USB2? If so look for any updated chipset/USB drivers.
2.) Secondly try defragging your harddrive. This will make it easier for the burning program to pull the data from your harddrive.
3.) Could be a hardware issue, faulty cable or faulty drive.
In terms of burning speeds this depends on the speed your drives will write at, not read.
We'll probably need some more info - makes/brands of disks used, software involved and manufacturers of the drives you have.