FWIW, I have a Korg D1600mkII digital recorder with a built-in cd burner. I bought some ProMedia 52x CD-R cds to burn with. My findings were that when set to the lowest speed, 4x, bad things happen, but when set to 16x, everything worked fine.
When I say "bad things happen", I mean that the resulting audio cd has some scratchy, crackly static on each of the songs, and worse, when you rip those songs to mp3, the static increases significantly. Once I changed the burn speed to 16x, the problem went away.
Just thought I'd share.