I just mastered a song for a friend. He was interested in hearing what different burn speeds would sound like. I have a Plextor 24/10/40 burner (IDE), so I can burn up to 24 X speed. Used
Wavelab 4.0 to author the disk.
We both agreed that 1X speed actually sounded the worse! Yikes! Anyway, I burned 1, 2, 4, 8, 10,12,16,20,24. We listened using a Masterlink to Sundholm mid-field monitors powered by a Hafler P-4000 amp, with Monster Studio Pro 1000 speaker cable (SP 1000 from the Masterlink to the Halfer too), and we were very hard pressed to hear much of a difference between the burns.
To be on the safe side, I don't burn final audio disks at over 8X on this burner. But for client copies or to check mixes, I don't shy away from 16X at all.
I am with atomictoyz on this one. Burn speeds were far more important to consider a few years ago, when IDE burners were still a relatively new thing. But the new breed of burners seem to do a very good job. I have never had a duplication facility deny a disk I have burned, and have a few projects that the label submitted to them go through just fine. So really, if your burner is no older than a couple of years, you probably don't have anything to worry about.
I am a Creep!