basicuffepuffe, welcome to the forum!
First, you should never write faster than your reader can read. As a reader slows down when errors occur, and readers only reach their top speeds in the outer parts of the CD, it is wise to write at a slower speed than the maximum reading speed of your reader.
If your writer and reader are connected to the same IDE channel, you better not use on-the-fly writing, as the IDE bus really can't handle this.
I don't know what software you are using, but if you happen to use Nero, you can do a speed check. You can find this option in the "burn" tab, before you start writing (it's called "Determine maximum speed"; make sure you don't use the wizard!)....