Slower speed in theory reduces jitter. Burning slower than 16x usually does not make sense with CDs though.
Keep in mind that it's an entirely different thing with DVDs though.
If you copy files the files don't lose anything as it's stored digitally. :disagree:
In theory, a copied CD should not lose quality either, as the data is stored digitally. The reasons for the "difference" heard by some are mostly unknown.