Burning speed questions

I am unsure if this is the best forum for this question, as it doesn't involve authoring or ripping, just burning.

I generally use Optical Quantum 4X discs. Imgburn says that the discs are rated as 4X, 6X, 8X, even though the label on the discs says 4X. I usually burn them at 4X but just tried 2 at 8X, and they seem to have burned OK and went through Imgburn's verify without disc errors.

So, should I burn them at 4X as the package says, or can I safely burn them at 8X?

TIA

SMK