Are 8x DVD media different from 4x media?

Hi!

Are 8x DVD media actually made in any different way than 4x DVD media?

Or is it just a matter of testing and sorting in the factory?

For example, computer processor manufacturers take CPUs off the same line, test them, and then sell them as “2000Mhz”, “2100Mhz” or “2200Mhz” only on the basis of the test results.