There is no "correct" answer to that question, since everyone has different standards, and every drive reads discs differently.
For me, on the LiteON 48125W testing at 40x (or Plextor Premium testing at 10x-24x CAV), I will accept C1 error rate averages of no higher then 2-2.5, and C1 error maximum values of no greater then 30-35. But I have *really* picky standards.
Punch Cards -> Paper Tape -> Tape Drive -> 8" Floppy Diskette -> 5 1/4" Floppy Diskette -> 3 1/2" "Flippy" Diskette -> CD-R -> DVD±R -> BD-R
The Progression of Computer Media