Now, might I ask that you re-explain the question? I’m having a bit of trouble following the query.
Are you saying that the discs you happened to get are supported at only 4x writing? Or that you only tried 4x writing?
And the discs were labeled as 6x, correct? Or is that what your burning software told you the maximum speed was? If the former, then your drive may have different support. If the latter, you know the maximum write speed for your drive.
Now, if you’re curious about read speeds, that’s something entirely different.
So, please clarify the query for us, if you don’t mind.