Nonetheless, slower burning means the pits are burned longer, and are more pronounced. It's not a tremendous difference, but for some players, it's enough of a difference. It's certainly worth a try.
"And one more thing, do disc labels affect playback at all? I can't remember faulty playback on a disc with a label on it, though I've played others that have labels with nary a problem. Any ideas? Thanks!"
Technically, anything that is added to a CD/DVD can potentially affect playback, generally by throwing off the center of gravity. If you are using labels that adhere to the disc, I would be very careful how you apply them. I print directly to my DVDs.
If every labelled disc you have doesn't play, and every labelled disc that is blank does play, then I'd say it's causing the problem. Other than that, it's hard to say without going through some real trial and error.
For what it's worth, I buy the generic Ritek DVDs (generally 8X), and have never burned a toaster. They are 30 cents apiece. My Toshiba 1200 is about 4 years old, and plays my DVDs fine.